Chemistry Unit 1

Question 1

Activated complex

Answer 1

An unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction.

Question 2

Activation energy

Answer 2

The energy required by colliding molecules to form an activated complex.

Question 3

Atomic number

Answer 3

The number of protons in a nucleus of an atom.

Question 4

Average rate

Answer 4

The change in mass or concentration of a reactant or product divided by the time interval during which the change occurs.

Question 5

Bonding continuum

Answer 5

A concept applied to bonding. Ionic and covalent bonding lie at opposite ends of the bonding continuum with polar covalent bonding.

Question 6

Catalyst

Answer 6

A substance which speeds up a reaction without itself being used up. It lowers the activation energy of the reaction.

Question 7

Collision geometry

Answer 7

A term used to describe the way reactants collide with each other.

Question 8

Collision Theory

Answer 8

A theory used to explain the factors which lead to a successful reaction. It explains how altering variables, such as temperature can affect the speed of the reaction. The theory requires reactants to collide, have the correct collision geometry and have a minimum (activation energy) before a reaction occurs.

Question 9

Covalent bonding

Answer 9

Bond formed between two atoms by the sharing pair of electrons. Usually occurs between non- metal atoms.

Question 10

Covalent molecular

Answer 10

A description of the structure and bonding in small molecules.

Question 11

Covalent network

Answer 11

A very strong and stable structure formed by certain elements and certain compounds. All the atoms are held together by strong covalent bonds. Consequently, covalent networks are all solids at room temperature and have very high melting points.

Question 12

Covalent radius

Answer 12

Measure of atomic size, half the distance between the nuclei of two covalently bonded atoms of an element. Covalent bond lengths between two atoms can be obtained by adding the appropriate covalent atomic radii.

Question 13

Delocalised electrons

Answer 13

Electrons which are not confined to a single orbital between a pair of atoms. Delocalised electrons are free to move away from the atom they came from.

Question 14

Electrochemical series

Answer 14

A list of chemicals arranged in order of their increasing ability to gain electrons, increasing oxidising power

Question 15

Electron

Answer 15

A particle that moves around the nucleus of an atom. It has a single negative charge but it’s mass is negligible compared to that of a proton or neutron.

Question 16

Electronegativity

Answer 16

The strength of the attraction by an atom of an element for its bonding electrons. If the electronegativities of two atoms sharing electrons are similar, the bond will be almost purely covalent. The greater the difference in electronegativities, the more likely the bond is to be polar covalent or even ionic.

Question 17

Functional group

Answer 17

A group of atoms of type carbon-carbon bond which provides a series of carbon compounds with its characteristic chemical properties.

Question 18

Group

Answer 18

A column of elements in the periodic table. The values of a selected physical property show a distinct trend of increase or decrease down the column. The chemical properties of the elements in the group are similar.

Question 19

Homologous series

Answer 19

A group of chemically similar compounds which can be represented by a general formula. Physical properties change progressively through the series for example the alkanes general formula CN H2 and +2 sure a steady increase in boiling point.

Question 20

Hydrogen bonding

Answer 20

Intermolecular forces of attraction. The molecules must contain highly polar bonds in which hydrogen atoms are linked to very electronegative nitrogen,oxygen and fluorine atoms. The hydrogen atoms are then left with a positive charge and are attracted to the electronegative atoms of other molecules. They are specific, stronger type of permanent dipole-permanent dipole interaction.