NCEA Level 2 Chemistry -Structure and bonding

Lewis Structure

A model that uses electron-dot structures to show how electrons (lone and paired) are arranged in molecules. Pairs of dots or lines represent bonding pairs.

molecule

two or more atoms held together by covalent bonds

multiple bond

a bond in which the atoms share more than one pair of electrons, such as a double bond or a triple bond.

ionic solid

solids composed of positively and negative ions held together by electrostatic attractions in a regular three-dimensional crystalline arrangement

ion

an atom or group of atoms that has a positive or negative charge obtained from losing or gaining electrons

atom

the smallest unit of an element that maintains the properties of that element

ionic bond

the attractive force between oppositely charged ions, which form when electrons are transferred from one atom to another

covalent bond

A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.

linear

shape of a molecule, atoms in a straight line eg CO2

bent

shape of a molecule, meaning angular or v-shaped. can have a bond angle of either 120 or 109 degrees

trigonal planar

an arrangement of atoms in the VSEPR model where the three pairs of electrons are placed 120 degrees apart on a flat plane.

trigonal pyramid

Shape of a molecule with three peripheral atoms not in the same plane as the central atom.Approx 109 degress, 3 bonding, 1 non bonding pair

tetrahedral molecule

a molecule in which four atoms are bound to a central atom, resulting in a tetrahedral shape; the atoms bonded to the central atom lie at the corners of a tetrahedron with 109° angles between them

VSEPR

Valence Shell Electron Pair Repulsion theory, stating that the three-dimensional molecular geometry about some central atom is determined by the electronic repulsion between its bonding and nonbonding electron pairs. Occupy optimal position for minimal repulsion.

The key phrase i need to use for VSEPR in the exam...

'the areas of electron density maximise separation to minimise repulsion to take the shape....'

polarity

a separation of electric charge in positive and negative reigions leading to a molecule having dipole

electronegativity

a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound

polar molecule

a molecule that has a slightly positive and negative end due to intermolecular polar bonds/dipoles do not cancel

non-polar molecule

molecule with no polar bonds or where polar bonds cancel their effects due to its symmetry

solute

substance that is dissolved in a solvent to make a solution

solvent

substance, usually liquid, that will dissolve another substance (the solute)

dipole

a separation of charge into positive and negative reigions that occurs in a chemical bond because of differences in the electronegativities of the bonded atoms

Boron trifluoride (lewis structure)

carbon tetrachloride (lewis structure)

Ozone (lewis structure)

Fluorine

most electronegative element

covalent network substances

Held together by an extended network of covalent bonds

A Substance that can conduct electricity

Contains either charged particles that can move or electrons that are free to move

A substance that has a high melting point

has strong bonds that take a lot of energy to overcome

ionic compound

A compound that consists of positive and negative ions

molecular substance

a substance that is made of molecules

metallic bonding

a bond formed by the attraction between positively charged metal ions and the electrons around them

Metallic substances

metal atoms interacting to form the metallic material

exothermic reaction

a chemical reaction that releases energy to its surroundings

endothermic reaction

A chemical reaction in which energy is absorbed

Enthalpy

the total energy of a system

breaking bonds is an

endothermic process

making bonds is an

exothermic process

molar mass unit

g/mol

mass unit

grams

moles (n) unit

mol

unit of Energy

kilojoule (kJ)