2.1 Atoms, Compounds, Molecules & Equations

Question 1

Which subatomic particle has a relative charge of +1 and is found in the nucleus of an atom?

Answer 1

Proton

Protons determine the atomic number of an element.

Question 2

Which subatomic particle has no charge but contributes to the mass of the nucleus?

Answer 2

Neutron

Neutrons add mass and help stabilise the nucleus.

Question 3

Which subatomic particle has a relative charge of −1 and occupies orbitals around the nucleus?

Answer 3

Electron

Electrons exist in orbitals arranged in energy levels around the nucleus.

Question 4

What is the small, dense central region of an atom that contains protons and neutrons called?

Answer 4

Nucleus

The nucleus contains nearly all the mass of the atom.

Question 5

True or False:

Most of the mass of an atom comes from electrons.

Answer 5

False

Almost all atomic mass comes from protons and neutrons in the nucleus.

Question 6

Fill in the blank:

Protons and neutrons have a relative mass of approximately _______ compared with each other.

Answer 6

1

Their masses are roughly equal on the relative scale used in chemistry.

Question 7

Fill in the blank:

The relative mass of an electron compared with a proton is approximately _______.

Answer 7

1/2000

This is why electrons contribute very little to atomic mass.

Question 8

Which particle determines the chemical behaviour of an element because of its arrangement around the nucleus?

Answer 8

Electron

Chemical reactions involve the rearrangement of electrons.

Question 9

True or False:

Protons, neutrons and electrons all have the same relative charge.

Answer 9

False

Their charges are +1, 0 and −1 respectively.

Question 10

What is the basic structure consisting of a nucleus surrounded by electrons?

Answer 10

Atom

Atoms are the fundamental building blocks of elements.

Question 11

What does the atomic (proton) number of an element represent?

Answer 11

Number of protons

The atomic number (Z) identifies the element.

Question 12

What does the mass number of an atom represent?

Answer 12

Total number of protons and neutrons

Mass number (A) counts nucleons in the nucleus.

Question 13

Fill in the blanks:

Mass number (A) is the sum of the number of _______ and _______.

Answer 13

protons; neutrons

Electrons are not included because their mass is negligible.

Question 14

Atoms of the same element that have different numbers of neutrons are known as what?

Answer 14

Isotopes

Isotopes have the same atomic number but different mass numbers.

Question 15

Why do isotopes of an element have the same chemical properties?

Answer 15

Same electron arrangement

Chemical behaviour depends on electrons, not neutrons.

Question 16

True or False:

Isotopes of an element have identical mass numbers.

Answer 16

False

Isotopes differ in the number of neutrons, so their mass numbers differ.

Question 17

Which technique is used to measure isotopic masses and relative abundances with high accuracy?

Answer 17

Mass spectrometry

A mass spectrometer separates ions based on mass-to-charge ratio.

Question 18

In a time of flight mass spectrometer, what process first converts atoms or molecules into ions?

Answer 18

Ionisation

Electrons are removed to form positive ions.

Question 19

NEW What is the traditional method of ionisation used in a TOF mass spectrometer for small molecules and atoms?

Answer 19

Electron gun

This involves bombarding gaseous samples with a beam of high - energy electrons fired from the gun

Question 20

During electrospray ionisation what is the sample dissolved in?

Answer 20

A polar, volatile solvent, such as water or methanol.

The solvent can act as a source of protons to facilitate the ionisation process M + H⁺ → MH⁺ where M represents a large molecule

Question 21

During electrospray ionisation, what occurs after the sample is dissolved?

Answer 21

The solution is pumped through a hypodermic needle, forming a fine mist of droplets with a +1 charge.

This process is considered a soft technique as generally no fragmentation occurs.

Question 22

After ionisation in a TOF mass spectrometer, what causes acceleration of the ions so they all have the same kinetic energy?

Answer 22

An electric field

The same kinetic energy is required to separate the ions, because if two ions have the same KE the heavier one will travel slower.

Question 23

What property of isotopes can be determined from the peak heights in a mass spectrum?

Answer 23

Relative abundance

Taller peaks indicate more abundant isotopes.

Question 24

What stage of a TOF mass spectrometer allows ions to separate according to their mass-to-charge ratio?

Answer 24

Ion drift

Due to having the same kinetic energy, lighter ions travel faster and reach the detector sooner.

Question 25

What stage of a **mass spectrometer** records the **arrival of ions** and produces a signal?

Answer 25

Ion detection ## Footnote The signal is proportional to ion abundance.

Question 26

What property of **isotopes** can be determined from the **peak heights in a mass spectrum**?

Answer 26

Relative abundance ## Footnote Taller peaks indicate more abundant isotopes.

Question 27

What occurs at the **ion detector** to measure the number of **ions** present in a **mass spectrometer**?

Answer 27

* Ions hit the detector. * Each ion gains an electron producing a current. * The **size of the current is relative to abundance.** ## Footnote The current can then be used to measure the relative abundance

Question 28

What quantity can be calculated from **isotopic masses** and their **abundances**?

Answer 28

Relative atomic mass ## Footnote Calculated using a weighted mean of isotopic masses.

Question 29

# Fill in the blanks: The **average mass of atoms of an element** accounting for **isotopic abundance** is called the _\_\_\_\_\_\_ _\_\_\_\_\_\_ _\_\_\_\_\_\_.

Answer 29

Relative atomic mass ## Footnote This value appears on the Periodic Table.

Question 30

# True or False: **Mass spectrometry** can be used to determine the **relative molecular mass** of a substance.

Answer 30

True ## Footnote The molecular ion peak gives information about molecular mass.

Question 31

What type of **ion** is typically formed when molecules are **ionised without fragmentation** in a mass spectrometer?

Answer 31

Molecular ion ## Footnote Represented as M⁺.

Question 32

Why do **lighter ions** reach the detector faster than **heavier ions** in a **TOF mass spectrometer**?

Answer 32

Higher velocity ## Footnote All ions have the same kinetic energy, so lighter ions move faster.

Question 33

When calculating **relative atomic mass** from **isotopic abundance**, what type of **mean** is used?

Answer 33

Weighted mean ## Footnote Each isotopic mass is multiplied by its relative abundance.

Question 34

How are **electrons arranged around the nucleus** of an atom in terms of **energy levels and orbitals**?

Answer 34

Electron configuration ## Footnote Describes the distribution of electrons in shells and sub-shells.

Question 35

What type of **sub-shell** contains a **maximum of two electrons**?

Answer 35

s sub-shell ## Footnote An s sub-shell contains one orbital.

Question 36

Which type of **sub-shell** contains **three orbitals** and can hold **up to six electrons**?

Answer 36

p sub-shell ## Footnote Each orbital holds two electrons.

Question 37

Which type of **sub-shell** contains **five orbitals** and can hold **up to ten electrons**?

Answer 37

d sub-shell ## Footnote d sub-shells first appear in the third shell.

Question 38

# Fill in the blank: A single **orbital** can hold a maximum of _\_\_\_\_\_\_ electrons.

Answer 38

2 ## Footnote The electrons must have opposite spins.

Question 39

What is the **energy required** to remove one electron from each atom in **one mole of gaseous atoms** called?

Answer 39

First ionisation energy ## Footnote Symbolised as IE₁.

Question 40

In what **state** must atoms be when defining **ionisation energy**?

Answer 40

Gaseous ## Footnote Ensures interactions between atoms do not affect the energy value.

Question 41

What is the **general equation** for the **first ionisation energy of sodium**?

Answer 41

Na(g) → Na⁺(g) + e⁻ ## Footnote Shows removal of one electron from a gaseous atom.

Question 42

What is the **general equation** for the **second ionisation energy of sodium**?

Answer 42

Na⁺(g) → Na2⁺(g) + e⁻

Question 43

What does a **large jump** between **successive ionisation energies** indicate?

Answer 43

Electron removed from a new inner shell. ## Footnote Inner shells are more strongly attracted to the nucleus so much more energy is needed

Question 44

# True or False: **Successive ionisation energies** always **increase**.

Answer 44

True ## Footnote Each electron is removed from a more positively charged ion.

Question 45

What does the **pattern of ionisation energies across Period 3** provide evidence for?

Answer 45

sub-shell structure ## Footnote Small drops occur when electrons enter higher-energy p orbitals.

Question 46

What feature in **ionisation energy data** indicates **electrons occupying paired orbitals**?

Answer 46

A small drop in ionisation energy between two successive values. ## Footnote Electron repulsion makes removal easier.

Question 47

# Fill in the blank: Across **Period 3**, the **first ionisation energy** generally _\_\_\_\_\_\_ from Na to Ar.

Answer 47

increases ## Footnote Nuclear charge increases while shielding is similar.

Question 48

Why does **ionisation energy** decrease down **Group 2** from Be to Ba?

Answer 48

Increased distance and shielding reduce attraction to the nucleus. ## Footnote Outer electrons are further from the nucleus and less strongly attracted.

Question 49

# True or False: **Ionisation energy** increases down a group because **atoms get larger**.

Answer 49

False ## Footnote Increased distance and shielding reduce nuclear attraction.

Question 50

What evidence do **successive ionisation energies** give about **electron arrangement in atoms**?

Answer 50

Shell structure ## Footnote Large jumps show when electrons begin to be removed from a lower shell.