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GCSE Chemistry · GCSEChapter 2 · Electron arrangement and the periodic table
GCSE · Chapter 2

Electron arrangement and the periodic table

By the end of this chapter you will be able to

  • Write the electron arrangement of an element from its atomic number
  • Use the periodic table to find the group and period of an element
  • Use the number of outer electrons to find the group number
  • Explain how Mendeleev arranged the elements, and why the modern table is ordered by atomic number
  • Compare metals and non-metals, and describe transition metals and noble gases

You should already know

  • Atomic number and the protons in an atom (Chapter 1)
  • The atom and its shells (Chapter 1)

Where this leads

  • Reactivity of metals and halogens (Chapter 3)
  • Ionic bonding from outer electrons (Chapter 4)
  • Covalent bonding and noble gas stability (Chapter 5)

GCSE Chemistry. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Describe electron shells and write electronic configurations for the first 20 elements, Explain that the periodic table is ordered by atomic number, with groups and periods, Predict properties of an element from its group, including the noble gases, Describe how the periodic table was developed, including Mendeleev’s gaps, Distinguish metals from non-metals, describe transition metals and explain the stability of noble gases.

Exercise P  Do you remember?

1
FHow many protons does a sodium atom have? Use the atomic number 11. Write the number.
2
FWhat is 2 + 2 x 3? Write the number.
3
FWhat is 2 cubed (23)? Write the number.
4
FWhat is 36 divided by 6? Write the number.
5
FWhich is the larger number, 5 or -3? Write the number.
2.1

Electron shells and electronic configuration

GCSE
Describe electron shells and write electronic configurations for the first 20 elements
Video lesson: Electron shells and electronic configurationComing soon
Context. Ruth is learning how atoms bond. Her teacher draws a shell diagram for chlorine and says, “The seven electrons in the outer shell matter most.” Ruth asks how she can work out the outer shell for any element. The answer is in the electron arrangement.

Electrons move in shells around the nucleus. For the first 20 elements, the first shell holds up to 2 electrons, and the second and third shells each hold up to 8 electrons. The electronic configuration lists the number of electrons in each shell, for example 2,8,1 for sodium.

11psodium (Na)electrons: 2, 8, 1
Sodium: electrons arranged in shells (not to scale)
17pchlorine (Cl)electrons: 2, 8, 7
Chlorine: electrons arranged in shells (not to scale)
Atomic numberElementElectron arrangementTotal electronsShells
1hydrogen (H)111
2helium (He)221
6carbon (C)2,462
10neon (Ne)2,8102
11sodium (Na)2,8,1113
12magnesium (Mg)2,8,2123
17chlorine (Cl)2,8,7173
18argon (Ar)2,8,8183
19potassium (K)2,8,8,1194
20calcium (Ca)2,8,8,2204
Electron arrangements of some elements

Key ideas

  • The first shell holds up to 2 electrons; the second and third hold up to 8 each.
  • The total of the numbers in the arrangement equals the atomic number.
  • The number of shells equals the period number.
  • The outer shell is the shell with the highest number.
Worked example 2.1.1
Write the electronic configuration of oxygen, atomic number 8. Write the numbers, separated by commas.

Method. Use the atomic number and fill the shells in order.

  1. Atomic number. Oxygen has 8 electrons.
    8 electrons
  2. Fill the first shell. The first shell takes 2.
    2 in shell 1
  3. Fill the second shell. The rest, 8 - 2 = 6, go in the second shell.
    6 in shell 2
  4. Write the answer.
    2,6

Check. 2 + 6 = 8, the atomic number of oxygen. ✓

Worked example 2.1.2
Write the electronic configuration of magnesium, atomic number 12. Write the numbers, separated by commas.

Method. Fill the shells in order and check the total.

  1. Atomic number. Magnesium has 12 electrons.
    12 electrons
  2. First two shells. Shell 1 takes 2 and shell 2 takes 8, a total of 10.
    2 + 8 = 10
  3. Remainder. The last 12 - 10 = 2 go in shell 3.
    2 in shell 3
  4. Write the answer.
    2,8,2

Check. 2 + 8 + 2 = 12. ✓

Worked example 2.1.3
How many shells does an argon atom have, and how many electrons are in its outer shell? Write two numbers, in this order.

Method. Find the configuration of argon.

  1. Configuration. Argon has atomic number 18, so its electrons are 2,8,8.
    2,8,8
  2. Shells. There are 3 shells.
    3 shells
  3. Outer shell. The outer shell is shell 3, which holds 8 electrons.
    8 in the outer shell
  4. Write the answer.
    3, 8

Check. The outer shell of argon is full. ✓

Watch out

Watch out: the outer shell is not always the one that is filled last. For the first 20 elements, use the rule: shell 1 takes 2, shells 2 and 3 take up to 8 each. Potassium (2,8,8,1) has a fourth shell with one electron.

Exam tip

Exam tip. Check your configuration: the numbers must add up to the atomic number. Write it with commas, as 2,8,1.

Exercise 2A  Electron shells and configurations

1
FHow many electrons can the first shell hold? Write the number.
2
FHow many electrons can the second shell hold, for the first 20 elements? Write the number.
3
FWrite the electronic configuration of sodium, atomic number 11. Write the numbers, separated by commas.
4
FWrite the electronic configuration of neon, atomic number 10. Write the numbers, separated by commas.
5
FWhich element has the electronic configuration 2,8,7? Write the name.
6
FWrite the electronic configuration of magnesium, atomic number 12. Write the numbers, separated by commas.
7
FHow many shells does a potassium atom have? Write the number.
8
FHow many electrons are in the outer shell of an argon atom? Write the number.
9
FHow many electrons are in the outer shell of a carbon atom? Write the number.
10
PSAn atom has the electronic configuration 2,8,3. What is its atomic number? Write the number.
11
PSWrite the electronic configuration of calcium, atomic number 20. Write the numbers, separated by commas.
12
PSPhosphorus has atomic number 15. Write its electronic configuration. Write the numbers, separated by commas.
13
RExplain why the electronic configuration of potassium is 2,8,8,1 and not 2,8,9, in one sentence. Accept any sentence that says the third shell is full with 8 electrons, so the extra electron goes into a fourth shell.
2.2

Groups, periods and the periodic table

GCSE
Explain that the periodic table is ordered by atomic number, with groups and periods
Video lesson: Groups, periods and the periodic tableComing soon
Context. A student is looking at the periodic table in the lab. “Why are some elements in the same column?” she asks. “And why do the rows end where they do?” The answer is in the number of electron shells and in the outer electrons.

The periodic table lists the elements in order of atomic number. Each vertical column is a group, and each horizontal row is a period. Elements in the same group have the same number of outer electrons, so they have similar chemical properties. The period number equals the number of electron shells.

12345670group numbers (1 to 7 and 0)11H2He23Li4Be5B6C7N8O9F10Ne311Na12Mg13Al14Si15P16S17Cl18Ar419K20Catransition metals (21 to 30)Period = row; group = column. Elements 1 to 20 shown.
The periodic table of the first 20 elements, with the group and period numbers
GroupOuter electronsNameExample
11alkali metalssodium, potassium
22alkaline earth metalsmagnesium, calcium
77halogenschlorine
08 (helium: 2)noble gasesneon, argon
Groups and their outer electrons

Key ideas

  • Periods are rows. The period number equals the number of electron shells.
  • Groups are columns. For groups 1, 2 and 3 to 7, the group number equals the number of outer electrons.
  • Group 0 (the noble gases) has a full outer shell.
  • The table is ordered by atomic number, the number of protons.
Worked example 2.2.1
Find the group and period of phosphorus, which has the electronic configuration 2,8,5. Write two numbers, group then period.

Method. Use the configuration to find the period and the group.

  1. Period. There are 3 shells, so phosphorus is in period 3.
    period 3
  2. Group. There are 5 outer electrons, so phosphorus is in group 5.
    group 5
  3. Check. The group and period are read from the table.
    group 5, period 3
  4. Write the answer.
    5, 3

Check. Phosphorus is in group 5, period 3. ✓

Worked example 2.2.2
Which element is in group 2 and period 3? Write the name.

Method. Find the column for group 2 and the row for period 3.

  1. Row. Period 3 is the third row.
    row 3
  2. Column. Group 2 is the second column.
    column 2
  3. Name. The element in row 3, column 2 is magnesium.
    magnesium
  4. Write the answer.
    magnesium

Check. Magnesium has 2,8,2, which has two outer electrons. ✓

Worked example 2.2.3
Which group does an element belong to if its electronic configuration is 2,8,8,2? Write the group number.

Method. Count the outer electrons.

  1. Outer shell. The outer shell has 2 electrons.
    2 electrons
  2. Group. Outer electrons equal the group number, so the group is 2.
    group 2
  3. Write the answer.
    2

Check. Calcium (atomic number 20) is in group 2. ✓

Watch out

Watch out: the periods are rows, not columns. A group is a column. Count the rows from the top and the columns from the left.

Exam tip

Exam tip. For groups 1 to 7, the group number tells you the number of outer electrons. For group 0, the outer shell is full.

Exercise 2B  Groups and periods

1
FWhat is a vertical column in the periodic table called? Write the word.
2
FWhat is a horizontal row in the periodic table called? Write the word.
3
FThe periodic table is ordered by atomic number. What does the atomic number count? Write the word.
4
FWhich group are the noble gases in? Write the number.
5
FWhich group are the alkali metals in? Write the number.
6
FWhich period is sodium in? Write the number.
7
FWhich group are the halogens in? Write the number.
8
FHow many outer electrons does calcium have? Write the number.
9
FWhich element is in group 1 and period 2? Write the name.
10
PSWrite the electronic configuration of boron, atomic number 5, then find its group. Write the group number.
11
PSWhich element is in the same group as lithium: sodium, neon or carbon? Write the name.
12
PSPhosphorus is in group 5 and period 3. Write its electronic configuration. Write the numbers, separated by commas.
13
RExplain why elements in the same group react in similar ways, in one sentence. Accept any sentence that says they have the same number of outer electrons.
2.3

Predicting properties from the group

GCSE
Predict properties of an element from its group, including the noble gases
Video lesson: Predicting properties from the groupComing soon
Context. A chemist is given a sample of an element and is told only that it is in group 1. “Can I predict how it will react?” she asks. The group tells her a lot: all group 1 elements have one outer electron, so they react in a similar way.

Elements in the same group have similar properties. The number of outer electrons decides how an element reacts. Group 1 elements (the alkali metals) have one outer electron and react by losing it. Group 7 elements (the halogens) have seven outer electrons and react by gaining one. The noble gases in group 0 have a full outer shell, so they are very unreactive.

GroupOuter electronsNameExample
11alkali metalssodium, potassium
22alkaline earth metalsmagnesium, calcium
77halogenschlorine
08 (helium: 2)noble gasesneon, argon
Groups 1, 2, 7 and 0 and their outer electrons

Key ideas

  • Group 1 elements have 1 outer electron.
  • Group 7 elements (halogens) have 7 outer electrons.
  • Group 0 (noble gases) have a full outer shell, and are unreactive.
  • Predictions use the group: an element in the same group will behave in a similar way.
Worked example 2.3.1
Lithium is in group 1. How many outer electrons does lithium have? Write the number.

Method. Use the group number for groups 1 and 2.

  1. Group. Lithium is in group 1.
    group 1
  2. Outer electrons. So it has 1 outer electron.
    1
  3. Write the answer.
    1

Check. Lithium’s configuration is 2,1. ✓

Worked example 2.3.2
Chlorine is a halogen. Predict how many outer electrons a chlorine atom has. Write the number.

Method. Halogens are in group 7.

  1. Group. Chlorine is in group 7.
    group 7
  2. Outer electrons. So it has 7 outer electrons.
    7
  3. Write the answer.
    7

Check. The configuration of chlorine is 2,8,7. ✓

Worked example 2.3.3
Argon is a noble gas. Why does it not react easily? Write the word.

Method. Think about the outer shell of argon.

  1. Configuration. Argon is 2,8,8, so its outer shell is full.
    full outer shell
  2. Conclude. A full outer shell is stable, so argon does not need to gain, lose or share electrons.
    stable
  3. Write the answer.
    stable

Check. Noble gases are unreactive because their outer shells are full. ✓

Watch out

Watch out: a prediction from the group is a prediction. It tells you what to expect, and you check it with evidence. Do not say an element will react “because it is in group 1” without linking the outer electrons.

Exam tip

Exam tip. To predict a property, write the group, then the number of outer electrons, then the link to the property.

Exercise 2C  Predicting properties from the group

1
FHow many outer electrons does an element in group 1 have? Write the number.
2
FHow many outer electrons does an element in group 7 have? Write the number.
3
FWhich group are noble gases in? Write the number.
4
FWhich halogen is a liquid at room temperature? Write the name.
5
FWhich halogen is a gas at room temperature? Give the name of one. Write the name.
6
FCalcium is in group 2. How many outer electrons does it have? Write the number.
7
FWhy is argon unreactive? Write one sentence. Accept any sentence that says its outer shell is full.
8
PSAn element has the configuration 2,8,8,2. Predict whether it is likely to be a noble gas. Write yes or no.
9
PSPredict the number of outer electrons of rubidium, which is in group 1. Write the number.
10
PSPredict the group of an element with the configuration 2,8,6. Write the number.
11
RLithium and sodium are both in group 1. Explain why they react in a similar way, in one sentence. Accept any sentence that says they both have one outer electron.
12
RExplain why a noble gas is less likely to form a compound than a halogen, in one sentence. Accept any sentence that says the noble gas has a full outer shell, so it does not need to gain or lose electrons.
2.4

The development of the periodic table

GCSE
Describe how the periodic table was developed, including Mendeleev’s gaps
Video lesson: The development of the periodic tableComing soon
Context. In 1869 a Russian chemist, Dmitri Mendeleev, was writing cards for each known element. He arranged the cards to make a pattern. “Where should the gaps go?” he asked. The gaps were a clever idea, and they were later filled.

Early tables ordered the elements by relative atomic mass. Mendeleev noticed that elements with similar properties appeared at regular intervals. He left gaps for elements he thought had not yet been discovered, and he predicted their properties. Some elements were put in an order that did not match their mass, so that they fitted with the elements that had similar properties.

PointWhat happenedDetail
1869Mendeleevarranged by relative atomic mass; gaps left for undiscovered elements
Tellurium and iodineswappedtellurium (Ar 127.6) is placed before iodine (Ar 126.9) so that iodine fits the halogens
Gallium and germaniumpredictedMendeleev predicted elements with the properties that these two later showed
Noble gasesadded laterdiscovered after the table was made, so they needed a new group
Modern tableatomic numberordered by the number of protons, which fixes most of the problems
Some points about the development of the periodic table

Key ideas

  • Mendeleev arranged the elements by relative atomic mass and left gaps for undiscovered elements.
  • He predicted properties for missing elements, and later discoveries (such as gallium and germanium) supported him.
  • Noble gases were discovered later, and were added as a new group.
  • The modern table is ordered by atomic number, which fixes the problems with the order of mass.
Worked example 2.4.1
In Mendeleev’s table, why was tellurium placed before iodine, even though tellurium is heavier? Write one reason.

Method. Compare the masses and the properties.

  1. Masses. Tellurium has a relative atomic mass of 127.6, and iodine is 126.9.
    Te 127.6, I 126.9
  2. Properties. Iodine has the properties of a halogen, so it had to go in the group 7 column.
    halogen
  3. Conclude. So the order was changed to fit the properties.
    order changed
  4. Write the answer.
    So that iodine fitted with the halogens, which have similar properties.

Check. Mendeleev chose properties over relative atomic mass. ✓

Worked example 2.4.2
Which element did Mendeleev need to leave a gap for? Give one reason for the gap in your answer. Accept any element that was not yet discovered in 1869 with a reason about the pattern of properties.

Method. Think about the pattern in the table.

  1. Pattern. Mendeleev saw a pattern of properties at regular intervals.
    pattern
  2. Gap. A missing element would fit the pattern, so a gap was left for it.
    gap left
  3. Write the answer.
    Accept any element that was not yet discovered in 1869 with a reason about the pattern of properties.

Check. Gallium and germanium were the elements that filled the gaps. ✓

Worked example 2.4.3
In the modern periodic table, which comes first, argon or potassium? Write the name.

Method. Compare the atomic numbers.

  1. Atomic numbers. Argon has atomic number 18 and potassium has atomic number 19.
    18 and 19
  2. Order. The table is ordered by atomic number, so the smaller number comes first.
    argon first
  3. Write the answer.
    argon

Check. Argon is in group 0 and potassium is in group 1. ✓

Watch out

Watch out: the modern table is ordered by atomic number, not relative atomic mass. Argon is placed before potassium, even though its relative atomic mass is larger.

Exam tip

Exam tip. When you explain Mendeleev’s table, mention the gaps and the predicted properties. Do not say that Mendeleev knew the atomic number.

Exercise 2D  Development of the periodic table

1
FWhich scientist first arranged the elements into a periodic table in 1869? Write the name.
2
FWhat property did Mendeleev use to order the elements? Write the words.
3
FWhy did Mendeleev leave gaps in his table? Write the words.
4
FName one element that Mendeleev predicted, using the gaps in his table. Write the name.
5
FWhat is the modern periodic table ordered by? Write the words.
6
FWhich element has atomic number 17? Write the name.
7
FWhich element has a higher relative atomic mass: tellurium or iodine? Write the name.
8
FWhy were the noble gases added to the table later? Write one sentence. Accept any sentence that says they were discovered after Mendeleev made his table.
9
PSExplain why the modern table, ordered by atomic number, is better than the early table ordered by relative atomic mass. Accept any sentence that says atomic number is unique to each element and avoids the reversed pairs.
10
RMendeleev predicted a gap for an element with properties like those of aluminium. Explain why he could do this, in one sentence. Accept any sentence that says the periodic pattern of properties showed a missing element.
2.5

Metals, non-metals, transition metals and noble gases

GCSE
Distinguish metals from non-metals, Describe transition metals and explain the stability of noble gases
Video lesson: Metals, non-metals, transition metals and noble gasesComing soon
Context. Two pupils sort the elements on a table. One group puts iron and copper together; the other puts oxygen and chlorine together. “Why did you split them like that?” the teacher asks. The answer is in where the elements sit on the table.

Metals are on the left and in the middle of the periodic table. Non-metals are on the right. Metals are usually shiny, conduct electricity and have higher melting points than non-metals. The transition metals are a block of metals between groups 2 and 3, including iron, copper and nickel. They are often hard, dense, and form coloured compounds. Many of them are useful catalysts.

Noble gases in group 0 have full outer shells. They are very unreactive, so they are used in lamps and balloons. Helium, neon and argon are examples.

PropertyMetalsNon-metals
positionleft and centre of the tableright of the table
melting point (typical)usually highusually low
conduct electricityyes, usuallyno (carbon graphite is an exception)
oxidesusually alkaline or basicusually acidic
outer electrons (typical)usually 1 to 3usually 4 to 8
Metals and non-metals compared
PropertyTransition metalsGroup 1 metals
positionblock between groups 2 and 3group 1
density and hardnessusually high and hardlow density, soft
melting pointusually highlow
coloured compoundsyes, oftenno
catalystoften (for example iron in the Haber process)not usually
Transition metals compared with group 1 metals
12345670group numbers (1 to 7 and 0)11H2He23Li4Be5B6C7N8O9F10Ne311Na12Mg13Al14Si15P16S17Cl18Ar419K20Catransition metals (21 to 30)Period = row; group = column. Elements 1 to 20 shown.metalnon-metal
Metals (blue) and non-metals (yellow) in the first 20 elements, with the transition metal block

Key ideas

  • Metals are on the left and centre; non-metals are on the right.
  • Transition metals sit in the block between groups 2 and 3.
  • Transition metals are often hard, dense, have high melting points, form coloured compounds and can act as catalysts.
  • Noble gases have full outer shells, so they are unreactive.
Worked example 2.5.1
Is iron a metal or a non-metal? Write the word.

Method. Use the position of iron on the table.

  1. Position. Iron is a transition metal in the middle of the table.
    middle
  2. Decide. Elements in the left and middle of the table are metals.
    metal
  3. Write the answer.
    metal

Check. Iron is a metal used in steel. ✓

Worked example 2.5.2
Name one property of transition metals that group 1 metals usually do not have. Write the words.

Method. Compare the two tables of properties.

  1. Compare. Transition metals are often hard and dense, and group 1 metals are soft.
    hard, dense
  2. Choose. Transition metals often form coloured compounds, and group 1 metals do not.
    coloured compounds
  3. Write the answer.
    coloured compounds

Check. Accept also: high melting point, or a catalyst. ✓

Worked example 2.5.3
Helium is used in balloons and is in group 0. Why is it unreactive? Write the words.

Method. Think about the outer shell of helium.

  1. Configuration. Helium has the configuration 2, so its only shell is full.
    full shell
  2. Conclude. A full outer shell is stable, so helium does not react.
    stable
  3. Write the answer.
    its outer shell is full

Check. Noble gases have full outer shells. ✓

Watch out

Watch out: a transition metal is not in group 1. It is in the block between groups 2 and 3, and it is a separate group of metals.

Exam tip

Exam tip. When a question asks for a property of transition metals, give a property that is typical, such as coloured compounds or use as a catalyst.

Exercise 2E  Metals, non-metals, transition metals and noble gases

1
FOn which side of the periodic table are most metals found? Write the word.
2
FOn which side of the periodic table are non-metals found? Write the word.
3
FIs copper a metal or a non-metal? Write the word.
4
FName a non-metal that is a gas at room temperature. Write the name. Accept any of: oxygen, nitrogen, chlorine, neon, argon.
5
FWhich block of metals sits between groups 2 and 3 of the periodic table? Write the words.
6
FName a property of transition metals. Write one property. Accept any of: hard, dense, high melting point, coloured compounds, catalyst.
7
FIron is used as a catalyst in the Haber process. Is iron a transition metal? Write yes or no.
8
FHow many electrons are in the outer shell of helium? Write the number.
9
FName one use of a noble gas that depends on it being unreactive. Write the name of a use.
10
PSWhich element is a metal: sulfur, sodium or chlorine? Write the name.
11
PSAn element has the configuration 2,8,6. Is it a metal or a non-metal? Write the word.
12
RExplain why the noble gases are unreactive, in one sentence. Accept any sentence that says they have a full outer shell, which is stable.
13
RA pupil says, “All transition metals are in group 1.” Explain why this is wrong, in one sentence. Accept any sentence that says transition metals form a block between groups 2 and 3.

Chapter summary

SkillMethod
ShellsThe first holds 2 electrons; the second and third hold up to 8 each (first 20 elements).
Electronic configurationThe number of electrons in each shell; the numbers add up to the atomic number.
Periods and groupsPeriods are rows (number = number of shells); groups are columns (number = outer electrons for groups 1 to 7).
MendeleevOrdered by relative atomic mass; left gaps and predicted missing elements.
Modern tableOrdered by atomic number, the number of protons.
Metals and non-metalsMetals on the left and centre; non-metals on the right.
Transition metalsA block between groups 2 and 3; hard, dense, coloured compounds, often catalysts.
Noble gasesGroup 0; full outer shells; very unreactive.

Can you…?

  • I can write the electronic configuration of the first 20 elements
  • I can find the group and period of an element from its configuration
  • I can predict properties from the number of outer electrons
  • I can explain how Mendeleev arranged the elements and why the modern table is ordered by atomic number
  • I can compare metals, non-metals, transition metals and noble gases

Key terms

electron shell
a layer of electrons around the nucleus of an atom
electronic configuration
the number of electrons in each shell of an atom, such as 2,8,1
group
a vertical column in the periodic table; elements in it have the same number of outer electrons
period
a horizontal row in the periodic table; its number is the number of electron shells
outer electrons
the electrons in the outermost shell of an atom
transition metals
the block of metals between groups 2 and 3
noble gases
the group 0 elements, which have full outer shells and are unreactive
relative atomic mass
the average mass of an atom of an element, compared with carbon-12

Exercise 2Z  Check-up

1
Write the electronic configuration of chlorine, atomic number 17. Write the numbers, separated by commas.
2
Which period is an element in if it has 3 shells? Write the number.
3
Which group is an element with 6 outer electrons in? Write the number.
4
Name the element with atomic number 20. Write the name.
5
Who arranged the elements in a periodic table in 1869, and left gaps? Write the name.
6
Which group are the halogens in? Write the number.
7
Name the group that contains the noble gases. Write the number.
8
Which element is in group 2 and period 2? Write the name.
9
An element has atomic number 15. Give its group and period. Write two numbers, group then period.
10
Explain why sodium and potassium react in a similar way, in one sentence. Accept any sentence that says they both have one outer electron.

Total 21 marks. Allow about 21 minutes.

Exercise 2X  Exam-style questions

1
FWrite the electronic configuration of potassium, atomic number 19. Write the numbers, separated by commas.[2 marks]
2
FState the group and period of an element with the configuration 2,8,1. Write two numbers, group then period.[2 marks]
3
FName the element in group 7 and period 2. Write the name.[1 mark]
4
FName the scientist who predicted properties for missing elements in his periodic table. Write the surname.[1 mark]
5
RExplain why the modern periodic table is ordered by atomic number rather than relative atomic mass. Write one sentence. Accept any sentence that says atomic number fixes the order, so argon (18) comes before potassium (19).[3 marks]
6
FDescribe one difference between metals and non-metals in their position on the periodic table. Write one sentence.[2 marks]
7
RExplain why neon is unreactive. Write one sentence. Accept any sentence that says its outer shell is full with 8 electrons.[2 marks]
8
FName two properties of transition metals. Accept any two of: hard, dense, high melting point, coloured compounds, catalyst.[2 marks]
9
PSAn unknown element is in group 2 of period 4. Write its electronic configuration. Write the numbers, separated by commas.[3 marks]
10
RExplain why elements in group 1 have similar chemical properties, in one or two sentences. Accept any answer that says they all have one outer electron, so they react in a similar way.[3 marks]
← Chapter 1: Atoms, elements, compounds and isotopesChapter 3: Reactivity of metals and halogens →

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