Definitions of Unit 1

Question 1

What is an atom?

Answer 1

the smallest particle of a chemical element that can exist.

Question 2

What is Atom Economy?

Answer 2

Measure of the proportion of reaction atoms that become part of the desired product in the balanced chemical equation.

Question 3

What is the Avogadro constant (L)

Answer 3

The number of atoms, molecules or ions in one mole of a given substance. It is the number of atoms in exactly 12 g of carbon-12 (6.02 x 10*23)

Question 4

What is a compound?

Answer 4

a substance formed from two or more elements chemically united in fixed proportions

Question 5

Percentage yield definition

Answer 5

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

Question 6

Relative atomic mass

Answer 6

: Average mass of an atom of an element, relative to 1/12 of the mass
of an atom of carbon-12.

Question 7

Relative formula mass:

Answer 7

: Average mass of a compound relative to 1/12 of the mass of an
atom of carbon-12. Relative formula mass refers to compounds that have a giant structure.

Question 8

Relative molecular mass

Answer 8

Average mass of a molecule relative to 1/12 of the mass of an
atom of carbon-12.

Question 9

State symbol:

Answer 9

State symbols show the physical state of the substance during the reaction,
they are usually in brackets: gas (g), liquid(I), solid(s) and aqueous(aq). Aqueous means the
substance is dissolved in water.

Question 10

Diatomic molecule:

Answer 10

: A molecule containing two atoms that are chemically bonded to each
other, e.g. Cl2.

Question 11

Electron subshell

Answer 11

Divisions of electron shells which are each at slightly different energy
levels. The subshells have different numbers of orbitals which can each hold up to two
electrons. The first four types of sub-shell are: s, p, d and f.

Question 12

Electronic configuration

Answer 12

: The distribution of electrons of an atom in its orbitals.
E.g. Ca: 1s22s22p°3s23p°4s2.

Question 13

First ionization energy:

Answer 13

: The energy required to remove 1 mole of electrons from 1 mole of
gaseous atoms to form 1 mole of gaseous 1+ ions. For example, Mg() > Mg () +e.
Isotope: Atoms of the same element with the same number of protons but a different
number of neutrons in the nucleus, e.g. 36CI and 37Cl.

Question 14

Mass spectrometry:

Answer 14

A technique that measures the mass to charge ratio of gaseous ions.
Mass spectrometry may be used after a mixture has been separated by GC to identify the
compounds present.

Question 14

Nuclear charge:

Answer 14

: Total charge of all the protons in the nucleus. It has the same value as the
atomic number. Increases as you go across the periodic table.

Question 15

Orbital:

Answer 15

A cloud of negative charge that can hold up to two electrons. Different orbitals have
different shapes.

Question 16

p orbital

Answer 16

A dumbbell shaped region in which up to two electrons can be found. There are
three p orbitals at right angles to each other, so in total the p subshell can hold up to 6
electrons.

Question 17

Periodicity:

Answer 17

Trends in properties of elements with increasing atomic number. The trends are
caused by the changes in element atomic structure.

Question 18

Quantum shell

Answer 18

Electrons orbit the nucleus in different energy levels known as shells. Each
energy level is assigned a principal quantum number, n. The shell which is found closest to
the nucleus has a value of n=1, the quantum number increases by one for each successive
shell.

Question 19

Relative abundance (of isotopes):

Answer 19

The percentage of atoms found within a naturally
occurring sample of an element that has a specific atomic mass.

Question 20

Relative peak height:

Answer 20

Found in mass spectra, indicating the relative abundance of the
substance that made the peak.

Question 21

s orbital:

Answer 21

Spherical and symmetrical regions found around the nucleus, which can each hold
up to two electrons.

Question 22

Second ionization energy:

Answer 22

: The energy required to remove 1 mole of electrons from each
ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions (could be asked for any
successive ionization energy).

Question 23

Shielding:

Answer 23

A decrease in the nuclear attraction experienced by an outer shell electron
caused by electron-electron repulsion between the outer shell electron and electrons from
adjacent quantum shells.

Question 24

Third ionization energy:

Answer 24

The energy required to remove 1 mole of electrons from each ion
in 1 mole of gaseous 2+ ions to form 1 mole of gaseous 3+ ions (could be asked for any
successive ionization energy).

Question 25

Mixture, give a definition

Answer 25

Mixture
Definition: A mixture is made of two or more substances (elements or compounds) that are physically combined but not chemically bonded.

Question 26

What is the difference between a mixture and a compound?

Answer 26

A mixture is a physical combination of two or more substances that retain their individual properties and can be separated by physical methods, such as filtration or distillation.
In contrast, a compound is a chemical combination of two or more elements in a fixed ratio, forming a substance with entirely new properties that can only be separated by chemical methods.

For example, saltwater is a mixture because the salt and water remain unchanged, while water (H₂O) is a compound because hydrogen and oxygen combine chemically to form a new substance. In conclusion, the key difference is that mixtures are physically combined and easy to separate, whereas compounds are chemically bonded and require chemical methods to break apart.

Question 27

Define the term mole

Answer 27

The amount of any substance containing the same number of particles as there are atoms in exactly 12g of carbon-12.

The mass of one mole of a substance is equal to its relative atomic or molecular mass in grams. For instance:

1 mole of carbon atoms has a mass of 12 grams (from its atomic mass of 12).
1 mole of water molecules (H₂O) has a mass of 18 grams (from 2 × 1 for hydrogen + 16 for oxygen).