Module 2.1 chemistry

What is an atom

An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in orbital shells

Where is almost all the mass of an atom?

In the nucleus, because protons and neutrons have approximately 1 relative mass while electrons have negligible mass

relative mass of a proton, neutron and electron

Proton: 1
Neutron: 1 (more accurately 1.001375)
Electron: 1/1836 in simplified model

charge of proton, neutron and electron

proton: 1
neutron: 0
Electron: -1

isotope

atoms of the same element with the same number of protons but different number of neutrons

Ion

A charged particle formed when an atom or group of atoms gains or loses electrons.

cation

A positively charged ion formed by the loss of electrons.

anion

A negatively charged ion formed by the gain of electrons.

Relative isotopic mass

The mass of an isotope relative to 1/12 of the mass of a carbon-12 atom.

Relative atomic mass (Ar​)

The weighted mean mass of an atom of an element relative to 1/12 of the mass of a carbon-12 atom.

Weighted mean

An average where different values are given different importance according to their abundance.]

Percentage abundance

The percentage of atoms in a sample that are a particular isotope.

Mass spectrometry

A technique used to determine the isotopic masses and abundances of elements.

Mass-to-charge ratio (m/z)

The mass of an ion divided by its charge.

Polyatomic ion

An ion containing two or more covalently bonded atoms with an overall charge.

Ionic compound

A compound made from positive and negative ions held together by electrostatic attraction.

Formula unit

The simplest whole-number ratio of ions in an ionic compound

Binary compound

A compound containing only two different elements.

Diatomic molecule

State symbol (s)
State symbol (l)
State symbol (g)
State symbol (aq)

Indicates that a substance is a solid, Liquid, Gas or aqueous (substance dissolved in water)

Balancing an equation

Adjusting the coefficients in front of formulae so that there are equal numbers of each type of atom on both sides.

Coefficient

A number placed in front of a chemical formula to balance an equation.

Roman numeral in an ionic name

Shows the charge/oxidation state of a variable-charge metal ion, e.g. iron(III) = Fe3+.