Chemistry - Foundations in Chemistry: Atomic Structure and Bonding definitions

Atomic Number

the number of protons in the nucleus of an atom

Bohr Model

describes an atom as a small dense nucleus with electrons orbiting around the nucleus. This model explains different periodic properties of atoms

Electron

a negatively charged subatomic particle which orbits the nucleus at various energy levels. The relative mass of an electron is 1/1836

Ion

a charged atom or molecule

Isotopes

atoms of the same element with the same number of protons and electrons but different numbers of neutrons. Isotopes of an element have different masses

Mass Number

the total number of protons and neutrons in the nucleus of an atom

Mass Spectrometry

an instrument which gives accurate information about relative isotopic mass and the relative abundance of isotopes

Neutron

a neutral subatomic particle found in the nucleus of an atom. The relative mass of a neutron is 1

Proton

a positively charged subatomic particle found in the nucleus of an atom. The relative mass of a proton is 1

Relative Abundance

the amount of one substance compared with another

Relative Atomic Mass

the weighted mean mass of an atom compared with 1/12th mass of an atom of carbon-12

Relative Isotopic Mass

the mass of an atom of an isotope compared with 1/12th mass of an atom of carbon-12

Relative Formula Mass

the mass of the formula unit of a compound with a giant structure. For example, NaCl has a relative formula mass of 58.44 g mol-1

Ammonium ion

an ion with the formula NH4+

Carbonate

an ion with the formula CO32-

Hydroxide

an ion with the formula OH-

Ionic Compound

a compound which is made up of oppositely charged ions that are held together by electrostatic forces

Nitrate

an ion with the formula NO3-

Silver ion

has the formula Ag+

Sulfate

an ion with the formula SO42-

Zinc ion

has the formula Zn2+

Amount of substance

the quantity that has moles as its units, used as a way of counting atoms. The amount of substance can be calculated using mass (n = m/M), gas volumes (n = pV/(RT)) or solution volume and concentration (n = CV)

Anhydrous

a crystalline compound containing no water

Atom Economy

a measure of the amount of starting materials that end up as useful products. A high atom economy means a process is more sustainable as there is less waste produced

Avogadro Constant (NA)

the number of particles per mole of substance (6.02 x 10^23 mol-1)

Composition by mass

the relative mass of each element in a compound

Empirical Formula

the simplest whole number ratio of atoms of each element present in a compound

Hydrated

a crystalline compound that contains water

Ideal Gas

a gas which has molecules that occupy negligible space with no interactions between them. The ideal gas equation is: pV = nRT

Molar Gas Volume

the volume of 1 mole of gas (units: dm3 mol-1)

Molar Mass

mass per mole of a substance (units: g mol-1)

Mole (mol)

the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12 isotope

Molecular Formula

the number and type of atoms of each element in a molecule

Percentage Yield

the percentage ratio of the actual yield of product from a reaction compared with the theoretical yield

Relative Molecular Mass

the average mass of one molecule of an element or compound compared to 1/12th the mass of an atom of carbon-12

Stoichiometry

the relative quantities of substances in a reaction

Water of Crystallisation

water molecules that form part of the crystalline structure of a compound

Acid

compounds that release H+ ions in aqueous solution. Common acids include: HCl, H2SO4, HNO3 and CH3COOH

Alkali

water soluble bases. Alkalis release OH- ions into aqueous solution. Common alkalis include: NaOH, KOH and NH3

Base

a substance that can accept H+ ions from another substance

Neutralisation

a reaction between H+ and OH-, forming water. This may be a reaction between an acid and a base to form a salt (types of bases include carbonates, metal oxides and alkalis)

Strong Acid

an acid that completely dissociates in solution

Titration

a technique used to determine the amount of one solution of a known concentration required to completely react with a known volume of another solution of unknown concentration

Weak Acid

an acid that only partially dissociates in solution

Oxidation

loss of electrons/ increase in oxidation number

Oxidation Number

a number that represents the number of electrons lost or gained by an atom of an element. A positive oxidation number indicates the loss of electrons. Roman numerals are typically used to indicate the oxidation number of elements that may have different oxidation states (e.g. iron(II) and iron(III))

Redox Reaction

a reaction in which one element is oxidised and another is reduced

Reduction

gain of electrons / decrease in oxidation number

Atomic Orbital

a region of space around the nucleus that can hold up to 2 electrons with opposite spins. There is 1 orbital in the s subshell, 3 orbitals in the p subshell and 5 orbitals in the d subshell. Orbitals are filled in order of increasing energy, with orbitals of the same energy occupied singly before pairing

Electronic Configuration

the arrangement of electrons into orbitals and energy levels around the nucleus of an atom / ion

Energy Level

the shell that an electron is in

Shell

the orbit that an orbital is in around the nucleus of an atom. The shell closest to the nucleus is the first shell. The outermost shell that is occupied by electrons is the valence shell

Sub-shell

a subdivision of the electronic shells into different orbitals. The types of subshell are s, p, d and f

Average bond enthalpy

the average energy required to break a bond, used as a measurement of the strength of a covalent bond. The average bond enthalpy is measured using a variety of molecules that contain a specific bond

Bonding pair

a pair of outer-shell electrons involved in bonding

Covalent bond

a strong bond formed between 2 atoms due to the electrostatic attraction between a shared pair of electrons and the atomic nuclei

Dative Covalent (Coordinate) bond

a type of covalent bond in which both of the electrons in the shared pair come from one atom

Electronegativity

the ability of an atom to attract bonding electrons in a covalent bond. This is often quantified using Pauling's electronegativity values. Electronegativity increases towards F in the periodic table

Electron Pair Repulsion Theory

pairs of electrons around a nucleus repel each other so the shape that a molecule adopts has these pairs of electrons positioned as far apart as possible. Lone pairs offer more repulsion than bonding pairs as they are closer to the nucleus of the central atom

Hydrogen Bonding

a type of intermolecular bonding that occurs between molecules containing N, O or F and a H atom of -NH, -OH or HF. A lone pair on the electronegative atom (N, O or F) allows the formation of a hydrogen bond

Intermolecular Forces

interactions between different molecules. Types of intermolecular forces including permanent dipole-dipole interactions and induced dipole-dipole interactions (both of these are also known as van der Waals' forces) as well as hydrogen bonding

Ionic Bond

electrostatic attraction between positive and negative ions

Ionic Compounds

compounds made up of oppositely charged ions. These compounds generally have high melting and boiling points. Typically, ionic compounds are soluble and can conduct electricity when liquid or aqueous (but not when solid)

Ionic Lattice

a giant structure in which oppositely charged ions are strongly attracted in all directions

Linear

the shape of a molecule in which the central atom has 2 bonding pairs

London (Dispersion) Forces

induced dipole-dipole interactions caused when the random movement of electrons creates a temporary dipole in one molecule which then induces a dipole in a neighbouring molecule

Lone Pair

a pair of outer-shell electrons not involved in bonding

Macroscopic Properties

properties of a bulk material rather than the individual atoms/molecules that make up the material

Non-linear

the shape of a molecule in which the central atom has 2 bonding pairs and 2 lone pairs

Octahedral

the shape of a molecule in which the central atom has 6 bonding pairs

Permanent Dipole

a permanent uneven distribution of charge

Polar Bond

a covalent bond that has a permanent dipole due to the different electronegativities of the atoms that make up the bond

Polar Molecule

a molecule that contains polar bonds with dipoles that don't cancel out due to their direction (must be unsymmetrical)

Pyramidal

the shape of a molecule in which the central atom has 3 bonding pairs and 1 lone pair

Simple Molecular Lattice

a solid structure made up of covalently bonded molecules attracted by intermolecular force (e.g. I2 and ice). These compounds generally have relatively low melting and boiling points and are typically insoluble in water but soluble in organic solvents. Molecular substances don't conduct electricity

Tetrahedral

the shape of a molecule in which the central atom has 4 bonding pairs

Trigonal bipyramidal

the shape of a molecule in which the central atom has 5 bonding pairs

Trigonal Planar

the shape of a molecule in which the central atom has 3 bonding pairs