Atomic structure

Question 1

Mass number (A)

Answer 1

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

Question 2

Atomic (proton) Number (Z)

Answer 2

number of protons in the nucleus of an atom
– it identifies the element
All atoms of the same element have the same number of protons

Question 3

Atoms

Answer 3

neutral atoms which have no overall charge the number of electrons is the same as the number of protons. The number of neutrons is just mass number minus atomic number

Question 4

Ions

Answer 4

Atoms form ions by gaining or losing electrons. Ions have different numbers of protons and electrons — negative ions have more electrons than protons, and positive ions have fewer electrons than protons.

Question 5

Anions

Answer 5

ion that has gained one or more electrons, acquiring a negative charge

Question 6

Cations

Answer 6

ion that has lost one or more electrons, acquiring a positive charge

Question 7

Zwitterion

Answer 7

molecule with functional groups, of which at least one has a positive and one has a negative electrical charge. The net charge of the entire molecule is zero

Question 8

Isotopes

Answer 8

element are atoms with the same number of protons but diff number of neutrons. E.G chlorine-35 and chlorine-37 are examples of isotopes.
They have different mass numbers, so they have different numbers of neutrons.
Their atomic number is the same.

Question 9

Radioisotopes

Answer 9

radioactive isotopes of an element.
They can also be defined as atoms that contain an unstable combination of neutrons and protons, or excess energy in their nucleus.
Radioactive isotopes have many useful applications.
In medicine, for example, cobalt-60 is extensively employed as a radiation source to arrest the development of cancer.
Other radioactive isotopes are used as tracers for diagnostic purposes as well as in research on metabolic processes.

Question 10

The decay of radioactive elements

Answer 10

occurs at a fixed rate

Question 11

The half-life of a radioisotope

Answer 11

time required for one half of
the amount of unstable material to degrade into a more stable material.
For example, Co-60 has a half-life of about 5 years while Ir-192 has a half-life of about 74 days

Question 12

Electron shells

Answer 12

Electrons have fixed energies. They move around the nucleus in certain areas of the atom called shells or energy levels. Each shell is given a number called the principal quantum number.
The further a shell is from the nucleus, the higher its energy and the larger its principal
quantum number.
Shells are divided up into
subshells.
Different electron shells have different numbers of sub-shells, which each have a different energy.
Subshells can be s sub-shells, p sub-shells, d sub-shells or f sub- shell

Question 13

Nuclear Force

Answer 13

force that binds the protons and neutrons in a nucleus together.
This force can exist between protons and protons, neutrons and protons or neutrons and neutrons.
This force is what holds the nucleus together

Question 14

Electromagnetic Force

Answer 14

Also called ‘the Lorentz force’, acts between charged particles, like negatively charged electrons and positively charged protons.
Opposite charges attract one
another, while like charges repel.
The greater the charge, the greater the force.

Question 15

Electronic Configurations

Answer 15

number of electrons that an atom or ion has, and how they are arranged is called its electron configuration.
It can be shown three ways.

Question 16

Aufbau Principle

Answer 16

electrons will occupy lowest energy orbital available

Question 17

Pauli’s Exclusion Principle

Answer 17

maximum of 2 electrons can occupy a single orbital

Question 18

Hund’s rule

Answer 18

e’s with same spin must occupy an orbital of equal energy before additional e’s with opposite spins can occupy the same orbital

Question 19

Periodic table

Answer 19

arranged into periods (rows) and groups(columns) by proton (atomic) number

Question 20

All the elements within a period

Answer 20

same number of electron shells (not counting subshells)

Question 21

All elements within a group

Answer 21

same number of electrons in their outer shell – so they have similar properties.
The group number tells you the number of electrons in the outer shell.

Question 22

exception to groups rule

Answer 22

group 0
All group 0 elements have 8 electrons in their outer shells apart from helium, which has two giving them full outer shells.

Question 23

Atomic Radius

Answer 23

decreases across a period. As the number of protons increases, the positive charge of the nucleus increases.
This means electrons are pulled closer to the nucleus making the atomic radius smaller.
The extra electrons that the elements gain across a period are added to the outer energy level, so they don’t really provide any extra shielding effect.
(Shielding is mainly provided by the electrons in the inner shells).
As you go down a group in the periodic table, the atomic radius gets larger.
This is because extra electron shells are added as you go down the group.

Question 24

The Shielding Effect

Answer 24

Electrons are attracted to protons in the nucleus of an atom.
The closer the electron is to the nucleus, the stronger the force of attraction.
The more protons in a nucleus, the more strongly an electron is
attracted to the nucleus.
Electrons are repelled by other electrons within an
atom.
If there are other electrons between a valence (outer) electron and the nucleus, the valence electron will be less attracted to the nucleus

Question 25

Electronegativity

Answer 25

the ability an atom has to attract other electrons. As you go across a period the electronegativity increases. This is because the nuclear charge increases, and the atomic radii decreases. There are more electrons but the increase in shielding is negligible because each extra electron enters the same shell so electrons will be more strongly attracted to the nucleus. Going down a group on the periodic table, the electronegativity of an element decreases because the increased number of energy levels puts the outer electrons very far away from the pull of the nucleus.

Question 26

Pauling scale

Answer 26

numerical scale of electronegativities based on bond- energy calculations for different elements joined by covalent bonds. There are no units with electronegativity. Linus Pauling designed a scale of electronegativity that ranks elements with respect to each other. So, for example, fluorine is a 4.0 in comparison to 0.7 for francium. These are the most and least electronegative elements respectively.