chemistry - Topic 1 — Atomic Structure and the Periodic Table

What is an atom?

The smallest part of an element that can exist.

What is an element?

A substance made of only one type of atom.

What is a compound?

Two or more different elements chemically bonded in fixed proportions.

What is a mixture?

Two or more substances not chemically combined; they can be physically separated.

How can a compound be broken into its elements?

By chemical reactions, not physical separation.

What is the basic structure of an atom?

A tiny nucleus of protons and neutrons surrounded by electrons in energy levels.

What do the symbols Na, K, Ca and Mg represent?

Sodium, potassium, calcium and magnesium.

What do the symbols Fe, Cu, Zn and Ag represent?

Iron, copper, zinc and silver.

Which elements have the symbols C, N, O, S and P?

Carbon, nitrogen, oxygen, sulfur and phosphorus.

Which elements have the symbols H, He, Ne and Ar?

Hydrogen, helium, neon and argon.

Which elements have symbols F, Cl, Br and I?

Fluorine, chlorine, bromine and iodine.

What does a chemical formula tell you?

The types and numbers or ratio of atoms in a substance.

Which method separates an insoluble solid from a liquid?

Filtration: solid remains as residue; liquid passes through as filtrate.

How can a dissolved solid be obtained from a solution?

Evaporate some solvent then cool so crystals form; filter and dry crystals.

How can a pure solvent be recovered from a solution?

Simple distillation: evaporate the solvent and condense its vapour.

When is fractional distillation used?

To separate miscible liquids with different boiling points using a fractionating column.

What does paper chromatography separate?

Soluble substances with different affinities for the mobile and stationary phases.

What is the stationary phase in paper chromatography?

The chromatography paper; the mobile phase is the solvent.

How is Rf calculated in chromatography?

Distance travelled by substance ÷ distance travelled by solvent front.

Why can substances in a mixture be physically separated?

They are not chemically bonded together.

What was Dalton's early atomic model?

Atoms were tiny, indivisible solid spheres.

What did Thomson's plum-pudding model propose?

Negative electrons embedded in a sphere of positive charge.

What did Rutherford's alpha-scattering experiment show?

Atoms are mainly empty space with a tiny, dense, positively charged nucleus.

Why did a few alpha particles deflect sharply or bounce back?

They approached the small, concentrated, positively charged nucleus.

How did Bohr improve the nuclear model?

He proposed electrons occupy specific energy levels around the nucleus.

Which scientist discovered evidence for the neutron?

James Chadwick.

Why did scientists change the model of the atom?

New experimental evidence contradicted earlier models.

Where are protons, neutrons and electrons found?

Protons and neutrons: nucleus; electrons: shells surrounding it.

What are the relative charges of proton, neutron and electron?

Proton +1; neutron 0; electron −1.

What are the relative masses of proton, neutron and electron?

Proton 1; neutron 1; electron about 1/1836.

What is atomic number?

Number of protons in the nucleus.

What is mass number?

Total number of protons and neutrons.

How do you calculate neutron number?

Mass number − atomic number.

Why does a neutral atom have no overall charge?

Its numbers of protons and electrons are equal.

What is an isotope?

Atoms of the same element with different numbers of neutrons.

How do you find electrons in a positive ion?

Number of protons − positive charge.

How do you find electrons in a negative ion?

Number of protons + magnitude of negative charge.

What is the approximate radius of an atom?

0.1 nm, or 1 × 10⁻¹⁰ m.

How does nucleus size compare with atom size?

The nucleus is less than 1/10,000 of the atom's radius.

What is relative atomic mass (Ar)?

Weighted mean mass of an element's atoms relative to 1/12 of a carbon-12 atom.

How do you calculate Ar from isotope abundances?

Sum of (isotope mass × percentage abundance) ÷ 100.

How many electrons fit in the first three shells for the first 20 elements?

First: 2; second: 8; third: 8, before the fourth shell fills.

What is the electron arrangement of sodium (11)?

2,8,1.

What is the electron arrangement of chlorine (17)?

2,8,7.

What is the electron arrangement of calcium (20)?

2,8,8,2.

Why do electrons occupy the inner shells first?

Electrons fill the lowest available energy levels.

How are elements ordered in the modern periodic table?

By increasing atomic number (proton number).

What does the group number indicate for Groups 1–7?

The number of electrons in the outer shell.

What does the period number indicate?

The number of occupied electron shells.

Why do elements in the same group react similarly?

They have the same number of outer-shell electrons.

How did Mendeleev improve the early periodic table?

He left gaps and sometimes reordered elements to group those with similar properties.

Why did Mendeleev's predictions gain acceptance?

Newly discovered elements matched the properties he predicted.

Where are metals and non-metals in the periodic table?

Metals mainly left and centre; non-metals mainly right.

How do metal atoms usually form ions?

They lose electrons, forming positive ions.

How do non-metal atoms usually form ions?

They gain electrons, forming negative ions.

How do metals and non-metals generally differ physically?

Metals often conduct and are malleable; non-metals usually conduct poorly.

Why are Group 0 noble gases unreactive?

Their outer electron shells are full and stable.

How does boiling point change down Group 0?

It increases as atoms become larger and intermolecular forces strengthen.

What are Group 1 metals called, and how many outer electrons?

Alkali metals; one outer electron.

How does Group 1 reactivity change down the group?

Increases: the outer electron is lost more easily due to shielding and distance.

What forms when an alkali metal reacts with water?

A metal hydroxide and hydrogen gas.

What is the word equation for sodium with water?

Sodium + water → sodium hydroxide + hydrogen.

What forms when Group 1 metals react with chlorine?

White metal chloride salts, e.g. sodium chloride.

What forms when Group 1 metals react with oxygen?

Metal oxides (simple GCSE description).

What are Group 7 elements called?

Halogens: reactive non-metals with seven outer electrons.

Why does Group 7 reactivity decrease down the group?

Increased shielding and distance make gaining an electron harder.

How do halogen melting and boiling points vary down Group 7?

They increase as molecules grow and intermolecular forces strengthen.

What happens when chlorine is added to potassium bromide solution?

Chlorine displaces bromine: chlorine is more reactive.

What are halogen molecules like?

Diatomic, e.g. Cl₂, Br₂ and I₂.

How do halogens react with metals?

They form ionic metal halides.

How do halogens react with other non-metals?

They form covalent compounds, e.g. hydrogen chloride.

How do transition metals compare with Group 1 metals?

Generally denser, harder, stronger, less reactive and higher melting points.

What is special about many transition-metal ions?

They can have different charges and form coloured compounds.

Why are transition metals often used as catalysts?

They can speed up reactions without being used up.

Give a transition metal used as a catalyst.

Nickel in hydrogenation or iron in ammonia manufacture.

Which common transition metals should you recognise?

Chromium, manganese, iron, cobalt, nickel and copper.

What are the symbols of lithium and beryllium?

Li and Be.

What are the symbols of boron and carbon?

B and C.

What are the symbols of nitrogen and oxygen?

N and O.

What are the symbols of fluorine and neon?

F and Ne.

What are the symbols of sodium and magnesium?

Na and Mg.

What are the symbols of aluminium and silicon?

Al and Si.

What are the symbols of phosphorus and sulfur?

P and S.

What are the symbols of chlorine and argon?

Cl and Ar.

What are the symbols of potassium and calcium?

K and Ca.

What are the symbols of hydrogen and helium?

H and He.