Ionic bonding

An atom is the smallest unit of an element that retains the chemical properties of that element.

Atoms form ions by becoming more stable: they lose electrons to form positive ions (cations), giving them more protons than electrons and a + charge, or they gain electrons to form negative ions (anions), giving them more electrons than protons and a − charge (memory: lose = +, gain = −).

Oxidation is the loss of electrons by a substance (often also described as gaining oxygen).

Reduction is the gain of electrons by a substance (often also described as losing oxygen).

When an atom loses electrons, it forms a positive ion (cation); when it gains electrons, it forms a negative ion (anion).

An atom has a central nucleus containing protons (positive charge) and neutrons (no charge), with electrons (negative charge) arranged in energy levels (shells) around the nucleus; overall, the atom is neutral because the number of protons equals the number of electrons.

An ionic bond is the electrostatic attraction between oppositely charged ions, formed when one atom loses electrons (becoming a positive ion) and another gains electrons (becoming a negative ion).

For main group elements, the group number tells you how many electrons are in the outer shell, so it predicts the ion charge: atoms lose or gain electrons to get a full outer shell. Group 1 → +1, Group 2 → +2, Group 3 → +3 (they lose electrons) Group 5 → −3, Group 6 → −2, Group 7 → −1 (they gain electrons) Group 0/18 → 0 (already stable, don’t form ions)

protons = mass number − neutrons

Electrons = protons

Neutrons = mass number − atomic number

A positive ion is formed when a metal atom loses one or more electrons from its outer shell, leaving it with more protons than electrons, so it has an overall positive charge.

A negative ion is formed when a non-metal atom gains one or more electrons into its outer shell, giving it more electrons than protons and therefore an overall negative charge.

The cross-over method is used to find the formula of an ionic compound by balancing charges: Write the ions with their charges Cross over the numbers from the charges to become the subscripts of the other ion Simplify the ratio if needed Drop the charge signs Example: Al³⁺ and O²⁻ → Al₂O₃

A dot and cross diagram is a model used to show the outer shell electrons of atoms and how they are shared or transferred in bonding, using dots for one atom and crosses for another to distinguish them.

An ionic compound is a substance made of positive and negative ions held together by strong electrostatic attraction (ionic bonds) between oppositely charged ions.

Balancing equations means adjusting the coefficients in front of substances so the number of each type of atom is the same on both sides of the equation, following the law of conservation of mass.

An ion is an atom or group of atoms that has gained or lost electrons and therefore carries an overall electric charge.

An ion is presented by writing the chemical symbol with its charge as a superscript (top right), e.g. Na⁺, Cl⁻, Ca²⁺.

The ending of an ion’s name indicates its composition: –ide → a single element ion (no oxygen) –ate → a compound ion containing oxygen, with more oxygen atoms –ite → a compound ion containing oxygen, with fewer oxygen atoms than the –ate ion

Top number → atomic number (protons) Large letters in the middle → chemical symbol (e.g. Na, O, Cl) Name underneath symbol → element name Bottom number → relative atomic mass (≈ mass number)

The atomic number is the number of protons in the nucleus of an atom; to work it out, you identify how many protons the atom has (or read it directly from the periodic table).

The mass number is worked out by adding the number of protons and neutrons in the nucleus of an atom.

An element is a pure substance made of only one type of atom and cannot be broken down into simpler substances by chemical means.