Simple Model of the Atom (AQA GCSE Combined Science: Trilogy: Chemistry): Flashcards

The metal comes first and the non-metal ends in -ide (e.g. sodium chloride, magnesium oxide).

False.

A compound has different properties from the elements it contains because the atoms are chemically combined in a new structure.

Find the charges of each ion, then use the smallest whole-number ratio that makes the overall charge zero. For example, Mg²⁺ and Cl⁻ combine as MgCl₂ because two Cl⁻ ions are needed to balance one Mg²⁺ ion.

A word equation shows a chemical reaction using the full names of reactants and products, written as:

reactants → products.

Reactants appear on the left-hand side of the arrow; products appear on the right. The arrow, spoken as "to form" or "produces", represents the conversion of reactants into products.

A symbol equation is balanced when the number of atoms of each element is the same on both sides of the equation.

False.

Changing the subscripts changes the substance itself. To balance an equation, change only the large coefficients written in front of the formulae.

Reaction conditions (such as temperature or pressure) or the name of a catalyst can be written above the arrow.

False.

State symbols must always be lowercase and enclosed in brackets. Writing the full word ("gas") or using upper case ("(G)") will not be credited in exams. The four state symbols are: (s), (l), (g) and (aq).

A half equation shows what happens to one species during a redox reaction, including balanced atoms, balanced charges, and the gain or loss of electrons.

OIL RIG: Oxidation Is Loss of electrons; Reduction Is Gain of electrons.

In a half equation, electrons on the left show the species is gaining electrons (reduction), and electrons on the right show it is losing electrons (oxidation).

An ionic equation shows only the particles that change during a reaction.

Spectator ions (those present but unchanged) are cancelled from both sides.

False.

Only aqueous compounds are split into ions. Solids, liquids and gases remain in their molecular form.

Copper(II) ions gain two electrons to form neutral copper atoms:

Cu²⁺ + 2e⁻ → Cu

Electrons are on the left, confirming this is reduction.

The negative charge (⁻) must be shown because it is essential for balancing the charges on both sides of the half equation. Writing e without the charge will not be credited in exams.

False.

The ionic equation is:

H⁺ (aq) + OH^- (aq) → H₂O (l).

Spectator ions are cancelled, leaving only the hydrogen and hydroxide ions combining to form water. The general word description is not an ionic equation.

A mixture contains two or more substances that are not chemically joined together. Mixtures can be separated by physical processes such as filtration, distillation, evaporation and chromatography.

Filtration separates an insoluble solid from a liquid or solution.

The liquid that passes through is the filtrate; the solid that remains is the residue.

Crystallisation separates a dissolved solid from a solution. After heating to evaporate the solvent, the saturated solution is cooled slowly so that crystals form.

False.

Fractional distillation is used when liquids have similar boiling points.

Simple distillation is used to separate a liquid from a dissolved solid, or when the boiling points differ significantly.

In a mixture, substances are not chemically bonded, so no bonds need to be broken to separate them. Physical processes exploit differences in properties such as boiling point, solubility or particle size.

Fractional distillation separates miscible liquids by exploiting differences in boiling point. The liquid with the lowest boiling point evaporates and is collected first.

Ink would dissolve in the solvent and run with the sample, contaminating the chromatogram.

If the solvent covers the spots, the sample will dissolve directly into it rather than travelling up the paper by capillary action.

False.

You should heat the solution to partially evaporate the solvent until a saturated solution forms, then leave it to cool slowly so crystals form. Heating to dryness damages the crystals and is not accepted in exams.

Different substances have different solubilities in the solvent and different attractions for the paper. More soluble substances travel further; less soluble substances are held back by the paper.

The plum pudding model, proposed by J.J. Thomson after his discovery of the electron in 1897, described the atom as a sphere of positive charge with negatively charged electrons embedded throughout it.

He expected all alpha particles to pass straight through (based on the plum pudding model). Instead, most passed through, some were deflected, and a small number bounced straight back.

Rutherford concluded that atoms are mostly empty space, with a tiny, dense, positively charged nucleus at the centre.

False.

Models are updated when new experimental evidence is found. The atomic model changed from solid sphere (Dalton) to plum pudding (Thomson) to nuclear (Rutherford) to shells (Bohr) as new discoveries were made.

Bohr proposed that electrons orbit the nucleus in fixed shells (energy levels) at specific distances from the nucleus. This explained why electrons do not spiral into the nucleus.

Chadwick discovered the neutron, a neutral particle in the nucleus. This explained the mass of atoms, which could not be accounted for by protons and electrons alone.

The nucleus is positively charged. Positive alpha particles passing close to the nucleus are repelled by the positive charge, causing deflection. A small number bounce straight back because they hit the nucleus almost head-on.

Atoms contain equal numbers of protons (+1) and electrons (−1), so the positive and negative charges cancel out.

False.

A proton has a relative charge of +1 (positive). A neutron is neutral (charge = 0) and an electron has a relative charge of −1.

Protons are Positive.

Neutrons are Neutral.

This leaves electrons as the negatively charged subatomic particle.

It contains 15 electrons. In a neutral atom, the number of electrons must equal the number of protons so that the charges cancel and the overall charge is zero.

Isotopes are atoms of the same element that have the same number of protons (and electrons) but different numbers of neutrons. They have the same chemical properties because they have the same electron configuration.

The atomic number (Z) is the number of protons in the nucleus; the mass number (A) is the total number of protons and neutrons. The number of neutrons = A − Z.

False.

Isotopes have the same chemical properties because they have the same number of electrons in their outer shells. Neutrons are neutral and only add mass.

Protons = 11 (= atomic number).

Electrons = 11 (neutral atom).

Neutrons = 23 − 11 = 12 (mass number − atomic number).

Almost all mass is in the nucleus, which contains protons and neutrons (relative mass = 1 each). Electrons have a very small mass (~1/1840 of a proton) and orbit the nucleus in shells.

False.

The mass number is always the larger number. Think: MASS = MASSIVE. The smaller number is the atomic (proton) number.

Protons = 9.

Electrons = 9 + 1 = 10 (gained 1 electron due to the 1− charge).

Neutrons = 19 − 9 = 10 (mass number − atomic number).

The relative atomic mass (A_r) is the average mass of an atom of an element, accounting for the abundance of its isotopes, relative to 1/12 the mass of a carbon-12 atom. It has no units because it is a ratio.

A_r is a ratio that compares the average mass of an atom to 1/12 the mass of a carbon-12 atom. Since it compares two masses, the units cancel out.

False.

A_r is a weighted average across all isotopes of an element. Since elements exist as a mix of isotopes, A_r can be a decimal (e.g. chlorine has A_r = 35.5).

The relative atomic mass is calculated as: the sum of (% abundance × mass of each isotope), divided by 100.

A_r = [(75 × 35) + (25 × 37)] ÷ 100 = (2625 + 925) ÷ 100 = 35.5

Period 3, Group 5.

The number of electron shells gives the period (3 shells = Period 3) and the number of outer-shell electrons gives the group (5 outer electrons = Group 5).

True.

Elements in the same group have the same number of outer-shell electrons, which is why they have similar chemical properties.

Na (Z = 11): 2,8,1

Cl (Z = 17): 2,8,7

2,8,8,1.

Potassium requires a fourth electron shell because the third shell is full at 8 electrons, leaving 1 electron in the fourth shell.

2,8.

Sodium loses its one outer-shell electron to form Na⁺, giving it the same electronic configuration as neon.