5: Atomic Structure

Question 1

What is an atom?

Answer 1

An atom is the smallest part of an element and the smallest unit of matter that still retains its chemical properties.

Question 2

What is an element? How many elements are there and how can they be presented?

Answer 2

An element is a substance that contains only one kind of atom. There are 118 elements, all listed in the periodic table, with 92 being naturally occurring (up to uranium). Each element has their own chemical symbol, consisting of an upper case letter and sometimes a lowercase letter.

Question 3

What are the chemical symbols of magnesium, lead, tin, mercury, silver, and gold?

Answer 3

Mg, Pb, Sn, Hg, Ag, Au

Question 4

What are the elements represented by chemical symbols Al, Br, Ca, K, and P?

Answer 4

Aluminium, bromine, calcium, potassium, phosphorus

Question 5

What are common characteristics of metals and what are some exceptions?

Answer 5

1. They are solids at rtp (room temperature & pressure) (exception: mercury is a liquid).
2. They are lustrous / shiny when there is a large and smooth surface.
3. They are usually strong and have a high density. (exception: group I metals)
4. They usually have high melting and boiling points. (exceptions: mercury and group I metals)
5. They are good conductors of heat and electricity.
6. They are malleable (can be pressed) and ductile (can be pulled into wires).

Question 6

What are the general physical properties of non-metals?

Answer 6

1. Most of them are gases or solids at room temperature (exception: bromine).
2. They usually have low melting points and boiling points compared to that of metals. (exception: graphite / diamond)
3. They are dull if they are solids (exception: diamond).
4. They are brittle if they are solids.
5. They are insulators of heat and electricity (exception: graphite conducts electricity).

Question 7

What is the meaning of brittle?

Answer 7

A brittle substance is hard and rigid on the surface but it breaks easily.

Question 8

What are the general physical properties of metalloids?

Answer 8

1. They are semi-conductors, meaning that they do not conduct electricity in a pure form, but they conduct electricity when mixed with impurities.
2. They have high melting and boiling points.
3. Their crystalline forms are shiny like metals.
4. They are brittle like non-metals.

Question 9

What are 2 examples of semi-metals and what are their characteristics?

Answer 9

Boron and silicon: They do not conduct electricity normally at rtp, but they conduct electricity well when mixed with impurities.
Silicon, as a semi-conductor, is used to make computer chips.

Question 10

What are protons, electrons, and neutrons?

Answer 10

Protons, electrons, and neutrons are sub-atomic particles that exist in every atom, except for hydrogen (hydrogen has no neutron). Protons carry a relative charge of +1 and have relative mass of 1, while neutrons are neutral in charge and have relative mass 1. Electrons have a relative charge of -1 and their relative mass is negligible (about 1/1800 of that of a proton).

Question 11

What is the overall charge of an atom and why?

Answer 11

The overall charge is neutral, because the number of protons and electrons are the same. The positive and negative charges from protons and neutrons respeictively balance one another (X cancel out).

Question 12

What is the nucleus of an atom and what are its properties?

Answer 12

The nucleus of an atom is made of protons and neutrons, having most of the atom’s mass. It occupies an extremely small amount of space relative to the atom, and the rest of the atom is mainly empty space. Electrons move freely around the nucleus.

Question 13

What is the atomic number?

Answer 13

The atomic number (Z) denotes the number of protons in an atom. Since there are an equal amount of protons and electrons in an atom, it represents the number of electrons in an atom as well.

Question 14

What is the mass number?

Answer 14

The mass number (A) denotes the relative mass of the atom, that is the sum of the number of neutrons and protons in the atom.

Question 15

How can we obtain the number of neutrons in an atom?

Answer 15

Number of neutrons in an atom = mass number - atomic number (A - Z)

Question 16

What are isotopes?

Answer 16

Isotopes are different atoms of the same element that have a different number of neutrons.

Question 17

What are the similarities and differences between two isotopes?

Answer 17

Isotopes have the same number of protons and electrons (thus the same atomic number), and the same chemical properties.
Isotopes have a different number od neutrons, so they have different mass numbers and different physical properties such as melting points and densities.

Question 18

What is the relative isotopic mass of atoms?

Answer 18

The relative isotopic mass of a particular isotope is the mass of an atom of the isotope, relative to 1/12 of the mass of a carbon-12 atom.
The mass of a carbon-12 atom is defined as 12.00.

Question 19

What is the relative atomic mass of an atom?

Answer 19

The relative atomic mass of an element is the weighted mean of the mass of an atom, taking into account the relative abundance and the relative isotopic mass of each isotope present in a naturally occuring sample of the element, relative to 1/12 of the mass of a carbon-12 atom.

Question 20

What are the characteristics of the electronic arrangements for elements 1-20?

Answer 20

Electrons are arranged in electron shells, while electron shells can hold different numbers of electrons. The maximum amount of electrons a shell can hold is 2n², but for elements 1-20, starting from the 3rd shell, the outermost valent shell can only hold 8 electrons. The period of the element is the number of occupied electron shells, while the group is the number of electrons in the valent shell.