Why do the elements in the same group react in similar ways?

Because their atoms have the same number of electrons in the outer shell, and it is the outer electrons that take part in reactions.

Why are the Group 0 elements almost completely unreactive?

Because their atoms already have a full outer shell, so there is no tendency to lose, gain or share electrons.

An atom has the electron arrangement 2,8,7. Predict how it will react and what ion it will form.

It will gain one electron to complete its outer shell, forming an ion with a single negative charge.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions State symbols in equations Conservation of mass, and changes of mass in open systems Exothermic and endothermic reactions, and reaction profiles Activation energy and why reactions need it Oxidation and reduction in terms of oxygen Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids The pH scale, acidity and alkalinity Measuring pH with indicators and pH meters Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Elements, Compounds and Mixtures

Reactions, electron arrangement and Mendeleev's table

3 things to know
Paper 3 (Chemistry)

Overview

Why a group reacts alike, the reactivity trends in Groups 1, 7 and 0, predicting how an atom with 2,8,7 reacts, how Mendeleev ordered the elements and left gaps, and ordering by atomic number.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why are the Group 1 elements so reactive?

Key term

Why does reactivity increase going down Group 1?

Key term

Why does reactivity decrease going down Group 7?

Questions from this subtopic

Each one with the model answer underneath.

1
Why do the elements in the same group react in similar ways?
Model answer
Because their atoms have the same number of electrons in the outer shell, and it is the outer electrons that take part in reactions.
2
Why are the Group 1 elements so reactive?
Model answer
Because each atom has just one outer electron, which is easily lost to form a positive ion.
3
Why does reactivity increase going down Group 1?
Model answer
Because the outer electron is further from the nucleus and better shielded by inner shells, so it is lost more easily.
4
Why does reactivity decrease going down Group 7?
Model answer
Because the outer shell is further from the nucleus and better shielded, so an extra electron is attracted less strongly.
5
Why are the Group 0 elements almost completely unreactive?
Model answer
Because their atoms already have a full outer shell, so there is no tendency to lose, gain or share electrons.
6
An atom has the electron arrangement 2,8,7. Predict how it will react and what ion it will form.
Model answer
It will gain one electron to complete its outer shell, forming an ion with a single negative charge.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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AMetals are on the left and in the centre, and non-metals are on the right-hand side.

BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

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