Key ideas Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher

What do elements in the same group have in common about their outer-shell electrons?

They have the same number of outer-shell electrons.

Why do elements in the same group tend to have similar chemical properties?

They have the same number of outer-shell electrons, which determine how atoms take part in chemical reactions.

What are all substances made from?

Atoms.

About how many different elements are there?

About 100.

What are the basic building blocks from which other substances are made?

Elements.

What is an atom?

The smallest part of an element that can exist as that element.

What is an element?

A pure substance made from only one type of atom.

What is meant by periodicity in the physical properties of elements?

Physical properties show recurring patterns when elements are arranged by increasing atomic number.

What helps explain variations in physical properties, such as melting point, across a period?

Bonding and structure help explain the variations; elements form different structures across a period.

As related patterns recur in later periods, how do outer-electron arrangements and the number of occupied shells compare?

Outer-electron arrangements recur, while the number of occupied electron shells changes.

What do outer-electron arrangements influence?

Bonding.

How are ions formed in ionic bonding?

Electrons are transferred between atoms, producing positive and negative ions.

How does an atom’s charge change when it loses or gains electrons?

Losing electrons makes it positive; gaining electrons makes it negative.

What holds ions together in an ionic structure?

Strong electrostatic attraction between oppositely charged ions.

What is a covalent bond?

A bond formed when atoms share a pair of electrons.

How do shared electrons hold covalently bonded atoms together?

The shared electrons are attracted to the nuclei of both atoms.

What two types of structure can contain shared electron pairs?

Molecules and giant covalent structures.

How can electron redistribution change which atoms are bonded in a reaction?

It can cause bonds to break or form.

Can electron-sharing changes occur alongside other reaction mechanisms?

Yes, they can occur alongside other reaction mechanisms.

What is a molecule?

A group of atoms bonded together in a particular spatial arrangement.

What two features can molecular shape affect that influence molecular behaviour?

The distribution of charge across the molecule and how closely molecules can interact.

What broad aspects of a molecule can its shape influence?

Its physical properties and chemical behaviour.

Besides shape-related features, what influences molecular behaviour?

The atoms and bonds present.

What is activation energy?

The minimum energy needed for a reaction to occur.

What two conditions must a collision meet to lead to a reaction?

Particles must collide with sufficient energy and a suitable orientation.

What determines the rate of a reaction in terms of collisions?

The frequency of successful collisions.

How can different energy barriers affect reaction rates?

Reactions with different barriers can occur at different rates.

What is a proton transfer reaction?

A reaction in which a hydrogen ion, $\ce{H+}$, moves from one species to another.

What are the roles of an acid and a base in proton transfer?

An acid donates a proton; a base accepts it.

What happens to hydroxide ions in aqueous neutralisation?

They accept protons to form water: $\ce{H+ + OH- -> H2O}$

What is conserved overall in a proton transfer reaction?

Atoms and charge.

What is an electron transfer reaction?

A reaction in which electrons move from one species to another.

What is the difference between oxidation and reduction in terms of electrons?

Oxidation is loss of electrons; reduction is gain of electrons.

Why do oxidation and reduction occur together?

Electrons lost by one species are accepted by another.

What particles can electron transfer produce?

Ions.

What type of substance can form in reactions involving electron transfer?

Ionic substances.

How is energy conserved in a chemical reaction?

Energy is transferred between the reacting system and its surroundings, but cannot be created or destroyed. Their total energy remains constant.

What happens to energy when chemical bonds are broken and formed?

Breaking bonds requires energy; forming bonds releases energy.

What happens when bond formation releases more energy than bond breaking requires?

Energy is transferred to the surroundings.

What happens when bond breaking requires more energy than bond formation releases?

Energy is taken in from the surroundings.