3A1 Basics of Atomic Structure, Elements, and Chemical Bonds

Question 1

What is an atom?

Answer 1

The smallest fundamental unit of matter that makes up all substances.

Question 2

Describe the structure of an atom.

Answer 2

Consists of a small, dense nucleus containing protons (positively charged) and neutrons (neutral).

This nucleus is surrounded by electrons (negatively charged) that orbit the nucleus.

Question 3

Where are protons located in an atom, and what is their charge?

Answer 3

• Location: found in the nucleus
• Charge: positive charge of +1

Question 4

Compare the mass of the subatomic particles.

Answer 4

• Protons: Approximately 1 amu
• Neutrons: Approximately 1 amu
• Electrons: Negligible mass compared to protons and neutrons

amu - atomic mass unit

Question 5

What does the atomic number of an atom refer to?

Answer 5

Refers to the number of protons it has.

Question 6

Where are neutrons located in an atom, and what is their charge?

Answer 6

• Location: in the nucleus
• Charge: no charge; they are neutral

Question 7

Where are electrons located in an atom, and what is their charge?

Answer 7

• Location: in the electron cloud surrounding the nucleus
• Charge: negative charge of -1

Question 8

What holds an atom together?

Answer 8

The attraction between the positively charged nucleus and the negatively charged electron cloud.

Question 9

How are elements defined?

Answer 9

By the number of protons in an atom’s nucleus, known as the atomic number.

Question 10

Who discovered the electron?

Answer 10

J.J. Thomson

The discovery was in the late 19th century.

Question 11

Who proposed the planetary model of the atom?

Answer 11

Ernest Rutherford

This was in the early 20th century.

Question 12

How did Erwin Schrodinger contribute to atomic theory?

Answer 12

He developed the quantum mechanical model of the atom, describing electrons in terms of probability clouds.

Question 13

The diagram shows an element of nitrogen. From the information provided, state the number of protons, neutrons, and electrons in one atom of Nitogren.

Answer 13

Protons: 7
Neutrons: 7
Electrons: 7

Question 14

How did atoms form after the Big Bang?

Answer 14

Through the cooling and combination of subatomic particles like protons, neutrons, and electron.

Question 15

What did Niels Bohr propose about electron orbits?

Answer 15

That electrons orbit the nucleus in fixed energy levels, or shells, and can jump between these levels when gaining or losing energy.

Question 16

Why are atoms studied using models?

Answer 16

They are too small to be observed directly even with the most powerful microscopes.

Question 17

Define an element and give an example.

Answer 17

• Definition: A pure substance composed of identical atoms that cannot be broken down into simpler substances by chemical means.
• Example: Oxygen (O₂)

Question 18

How are elements different from compounds?

Answer 18

• Elements are made of single types of atoms.
• Compounds are made of different types of atoms chemically bonded together.

Question 19

What is the Periodic Table?

Answer 19

A chart that organizes all known elements based on their atomic number, electron configuration, and properties.

Question 20

How many natural elements exist, and how many have been artificially created?

Answer 20

• 92 natural elements.
• 26 artificially created in laboratories.

Question 21

What categories do elements fall into on the Periodic Table?

Answer 21

• Metals
• Non-metals
• Metalloids based on their properties like conductivity and appearance

Question 22

What determines an element’s chemical symbol?

Answer 22

It is based on either one or two letters derived from its name.

E.g. H for hydrogen or Na for sodium.

Question 23

How do elements combine to form substances like water or sugar?

Answer 23

Through chemical bonds.

E.g. water (H₂O) or sugar (C₆H₁₂O₆).

Question 24

How do electrons affect the properties of an element?

Answer 24

The number and arrangement of electrons determine an element’s reactivity, chemical bonding behavior, and many of its physical properties.

Question 25

What are isotopes of an element?

Answer 25

These are atoms of the same element with different numbers of neutrons, leading to variations in atomic mass but similar chemical properties.

Question 26

What are noble gases, and why are they unique?

Answer 26

A group of elements that are typically inert, have full outer electron shells, making them stable and unreactive under normal conditions.

Question 27

What is the fundamental difference between mixtures and pure substances in chemistry?

Answer 27

• Mixtures: Are composed of substances that are not chemically bonded and can be separated physically.
• Pure substances: have fixed compositions and cannot be separated into simpler substances by physical means.

Examples of pure substances are elements and compounds.

Question 28

How do compounds differ from elements?

Answer 28

• Compounds are pure substances composed of atoms of two or more different elements in fixed ratios.
• Unlike elements, compounds can be decomposed into their constituent elements through chemical reactions.

Question 29

What are the types of chemical bonds that hold atoms together in compounds?

Answer 29

• Ionic bonds: Electrostatic attraction between ions of opposite charges.
• Covalent bonds: Sharing of electrons between atoms.

Question 30

Describe the properties of an ionic compound.

Answer 30

• Formed between metals and nonmetals.
• Have high melting points.
• Conduct electricity when dissolved in water.
• Consist of ions held together by ionic bonds (e.g., NaCl).

Question 31

Describe the properties of a covalent compound.

Answer 31

• Formed between nonmetals.
• Have lower melting points.
• Do not conduct electricity well.
• Are held together by covalent bonds (e.g., CO₂).

Question 32

Provide an example of a compound and an element.

Answer 32

• Compound: Carbon dioxide (CO₂), made of carbon and oxygen atoms in a fixed ratio.
• Element: Helium (He), composed of identical helium atoms.

Question 33

Why are elements reactive and how do they combine to form compounds?

Answer 33

• They are reactive because they seek to complete their electron shells.
• They combine with other elements to form stable compounds through electron transfer (ionic bonds) or electron sharing (covalent bonds).

Question 34

What role do electrons play in chemical bonding?

Answer 34

They are involved in chemical bonding by either being transferred between atoms (ionic bonding) or shared between atoms (covalent bonding).

This interaction stabilizes atoms into compounds.

Question 35

How do the properties of compounds differ from those of their constituent elements?

Answer 35

Compounds exhibit properties distinct from their component elements.

For example, sodium (a reactive metal) and chlorine (a toxic gas) combine to form sodium chloride, a stable compound commonly known as table salt.

Question 36

Explain the difference between molecules and compounds.

Answer 36

• Molecules are formed when two or more atoms bond together, regardless of whether they are the same or different elements.
• Compounds specifically refer to molecules composed of atoms from different elements.

Question 37

Why are ionic compounds good conductors of electricity when dissolved in water?

Answer 37

They dissociate into ions when dissolved in water, allowing for the free movement of charged particles (ions), which facilitates electrical conductivity.

Question 38

What is meant by ‘periodic table notation’?

Answer 38

It is a method of presenting the elements, whereby characteristics such as element name, symbol, atomic number, atomic weight, and electron configuration can be easily identified at a glance.

Periodic table notation is used in the periodic table.

Question 39

When is a subscript used in periodic table notation?

Answer 39

When more than one atom of a particular element is present, subscripts are used to denote the exact number of atoms present.

For example, a molecule of oxygen has two atoms, so it is written as O₂.

By convention, subscripts are always written to the bottom right of the element it is referring to.

Question 40

What does a chemical formula tell you?

Answer 40

They indicate all the elements within a molecule, as well as the number of atoms of each element.

Question 41

The chemical formula for methane is CH₄. List the number of atoms of each elements present in methane.

Answer 41

Carbon: 1
Hydrogen: 4

Question 42

When is a coefficient used in periodic table notation?

Answer 42

When there is more than one molecule of a substance, the number of molecules is indicated with a coefficient.

The coefficient is written immediately to the left of the molecule it is referring to. For example, two molecules of water would be written as: 2H₂O.

Question 43

Define an ion.

Answer 43

It’s an atom or molecule that has gained or lost one or more electrons, resulting in a net electric charge.

An ion has a positive charge if it has lost electrons (cation); a negatively charged ion (anion) results from gaining electrons.

Na+1 is the chemical formula for a sodium ion, which has a positive charge of one unit.

Question 44

Distinguish between subscripts written on the bottom left and bottom right of the chemical symbol.

Answer 44

Bottom left: Represents the atomic number of the element.
Bottom right: Indicates the number of atoms of the element present in the molecule.

Question 45

Which image (I, II or III) in the diagram represents a ‘pure substance’?

Answer 45

Image I

This is an element.