1.2 atomic structure

Question 1

Atomic number

Answer 1

The number of protons in (the nucleus
of) an atom.

Question 2

mass number

Answer 2

The total number of protons and
neutrons in (the nucleus of) an atom.

Question 3

RAM

Answer 3

The average (weighted mean) mass
of an atom of an element relative to
one-twelfth of the mass of an atom of
carbon-12.

Question 4

RIM

Answer 4

The mass of an atom of an isotope of
an element relative to one-twelfth of
the mass of an atom of carbon-12.

Question 5

isotopes

Answer 5

Atoms which have the same atomic
number but a different mass number
(contain the same number of protons
but a different number of neutrons).

Question 6

RMM

Answer 6

The average (weighted mean) mass
of a molecule relative to one-twelfth of
the mass of an atom of carbon-12.

Question 7

RFM

Answer 7

The average (weighted mean) mass
of a formula unit relative to one-
twelfth of the mass of an atom of
carbon-12

Question 8

first ionisation energy

Answer 8

The energy required to convert one
mole of gaseous atoms into gaseous
ions with a single positive charge.

Question 9

second ionisation energy

Answer 9

The energy required to convert one
mole of gaseous ions with a single
positive charge into gaseous ions with a double positive charge

Question 10

third ionisation energy

Answer 10

The energy required to convert one
mole of gaseous ions with a double
positive charge into gaseous ions with
a triple positive charge.

Question 11

ground state

Answer 11

An electronic configuration in which
all the electrons are in the lowest
(available) energy levels.

Question 12

ions

Answer 12

charged particles formed when an atom loses or gains electrons

Question 13

mass spectrometers

Answer 13

A mass spectrometer is used to:
Determine relative atomic mass
Determine isotopic abundance
The mass spectrometer separates atoms according to their mass. A sample of the
element is placed in the machine and a trace is printed out which gives the relative
isotopic mass present and the percentage abundance.
The trace that is printed out is called a mass spec

Question 14

carbon 12 standard

Answer 14

When we measure something we compare it to a known quantity. Chemists
compare the masses of atoms with the mass of the carbon-12 isotope – it is called
the carbon 12 standard; its mass is 12.0000. For example, a magnesium atom is
twice as heavy as a carbon-12 atom and was assigned a mass of 24.
The carbon-12 isotope was chosen as the standard as it is a solid at room
temperature, stable and easy to transport and store.

Question 15

an orbital

Answer 15

a region within an atom can hold up to two electrons with opposite spin

Question 16

exceptions (cu and cr)

Answer 16

Chromium and copper have unusual electronic configurations.
24Cr is not 1s2 2s2 2p6 3s2 3p6 3d4 4s2 as expected but it is 1s2 2s2 2p6 3s2 3p6 3d5
4s1
.
This is due to the fact that two half-filled subshells are more stable due to the
equal distribution of charge around them.
29Cu is not 1s2 2s2 2p6 3s2 3p6 3d9 4s2 as expected but is 1s2 2s2 2p6 3s2 3p6 3d10
4s1
.
This is because a half-filled 4s and full 3d are more stable.
These are the ONLY two exceptions.

Question 17

shape of s orbital

Answer 17

spherical

Question 18

shape of p orbital

Answer 18

dumb bell

Question 19

what is an s block element

Answer 19

An s-block element is an element which has an atom with highest energy/outer
electron in an s-subshell.

Question 20

what is a d block element

Answer 20

An d-block element is an element which has an atom with highest energy/outer
electron in an d-subshell.

Question 21

what is a p block element

Answer 21

A p-block element is an element which has an atom with highest energy/outer
electron in a p-subshell.

Question 22

successive ionisation energies

Answer 22

Successive ionisation energies are a measure of the energy required to remove
each electron in turn. Therefore, an element has as many ionisation energies as it
has electrons.

Question 23

factors that affect ionisation energy

Answer 23

What factors affect ionisation energy?
Negative electrons are held in their shells by their attraction to the positive nucleus.
To remove an electron, ionisation energy must be supplied. Electrons in the outer
shell are removed first and require the least ionisation energy as they experience the
least attraction from the positive nucleus. The following four factors are used to
explain trends in ionisation energies:
(1) distance of outermost electron from the nucleus (atomic radius)
The greater the atomic radius, the smaller the nuclear attraction experienced
by the outer electrons.
(2) size of positive nuclear charge
The greater the nuclear charge the greater the attractive force on the outer
electrons.
(3) shielding (by inner shells of electrons)
Inner shells of electrons repel the outer shell electrons. Shielding reduces the
attraction from the positive nucleus on the outer shell electrons.
(4) stability of filled and half-filled subshells

Question 24

trends in 1st ionisation energy down a group

Answer 24

Trend in 1st ionisation energies down a group
Ionisation energy decreases as you move down a group because:
 increase in atomic radius
 increase in shielding
The number of electron shells increase as you move down a group and so the
distance of the outermost electron from the nucleus increases and so there is a
weaker force of attraction on the outer shell electrons.
There are many more inner shells of electrons and so more shielding, so the outer
shell of electrons is held less tightly by the nuclear charge.

Question 25

trends in 1st ionisation energy across a period

Answer 25

Ionisation energy increases as you move across a period
 increase in nuclear charge
 no change in shielding
The nuclear charge (number of protons in the nucleus) is increasing so there is a
greater attraction pulling the outer shell of electrons closer to the nucleus and so the
distance from the nucleus decreases (atoms get smaller as you move across a
period).
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The shielding effect is constant since electrons are being removed from the same
shell.