Y9 Chemistry: Atomic Structure

How is an atom defined in atomic structure?

An atom is the smallest part of an element that can exist.

What is an element, and what are some examples?

An element contains only one type of atom (e.g., $Fe$, $Mg$, or $H_2$).

What is a molecule, and what examples illustrate it?

A molecule contains two or more atoms bonded together, which can be the same or different (e.g., $H_2$, $O_2$, or $H_2O$).

How is a chemical compound defined?

A compound contains two or more different types of atoms chemically bonded together (e.g., $H_2O$ or $CO_2$).

Based on this diagram of an atom, where are the protons, neutrons, and electrons located?

Protons and neutrons are located at the centre of the atom in the nucleus, while electrons move very fast around the nucleus in orbital paths called shells.

Why is the mass of an atom almost entirely contained within the nucleus?

Because the mass of an electron is negligible, so the atom's mass is concentrated where the protons and neutrons are located.

What rule governs the capitalisation of two-letter chemical symbols on the Periodic Table?

The first letter is always written in uppercase and the second letter is always in lowercase (e.g., sodium is $Na$, not $NA$).

Which elements must be written as diatomic molecules because they exist in nature as two atoms joined together?

$H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, and $I_2$.

What does the atomic number indicate, and what occurs if it changes?

It tells the number of protons, which is unique for each element. If the number of protons changes, the identity of the element changes.

What information does the mass number provide?

The mass number tells the total number of both protons and neutrons in the nucleus.

In this Periodic Table tile for magnesium, what do the numbers $12$ and $24$ represent?

$12$ is the atomic number (number of protons) and $24$ is the mass number (total number of protons and neutrons).

What are the relative masses and relative charges of a proton, neutron, and electron?

Proton: relative mass $1$, relative charge $+1$; Neutron: relative mass $1$, relative charge $0$; Electron: relative mass $0.0005$, relative charge $-1$.

How is an electronic configuration represented, and what are the configurations of magnesium ($12$ electrons) and chlorine ($17$ electrons)?

By writing the number of electrons in each energy level separated by commas: Magnesium is $2, 8, 2$ and Chlorine is $2, 8, 7$.

According to the electron shell model shown, what is the maximum number of electrons each of the first three shells can accommodate?

First shell: $2$ electrons; Second shell: $8$ electrons; Third shell: $8$ electrons.

What element and electronic configuration are shown in this electron shell diagram?

Magnesium with an electronic configuration of $2, 8, 2$.

What is the relationship between an element's group number and its electronic configuration?

The group number is always the same as the number of electrons in the outer shell (e.g., magnesium is in group $2$ with $2$ outer electrons; chlorine is in group $7$ with $7$ outer electrons).

Why do elements in the same group of the Periodic Table have similar chemical properties?

They have similar chemical properties because they have the same number of electrons in their outer shell, which determines how an element reacts.

Why are the Noble gases very unreactive?

They have a full outer energy level with $8$ electrons, which makes them very stable with no need to gain or lose electrons.

What is the definition of valency?

Valency is the 'combining power' of an element, representing how many other elements or groups of elements it can bond to.

What are the standard valencies for groups 1, 2, 3, 5, 6, and 7 of the Periodic Table?

Group 1: $1$; Group 2: $2$; Group 3: $3$; Group 5: $3$; Group 6: $2$; Group 7: $1$.

Which ions and elements listed in the notes have a valency of $1$?

Hydroxide ($OH$), Nitrate ($NO_3$), Hydrogen ($H$), Ammonium ($NH_4$), Hydrogen Carbonate ($HCO_3$), and Silver ($Ag$).

Which ions and elements listed in the notes have a valency of $2$?

Carbonate ($CO_3$), Sulphate ($SO_4$), Zinc ($Zn$), Lead ($Pb$), Copper (II) ($Cu$), and Iron (II) ($Fe$).

Which ions and elements listed in the notes have a valency of $3$?

Aluminium ($Al$), Phosphate ($PO_4$), and Iron (III) ($Fe$).

How are valencies used to deduce the chemical formula of calcium oxide and water?

Calcium ($2$) and oxygen ($2$) balance out directly to give $CaO$. Hydrogen ($1$) and oxygen ($2$) do not balance, requiring two hydrogens to balance the oxygen valency of $2$, giving $H_2O$.

What is the essential rule regarding subscripts and coefficients when balancing chemical equations?

You cannot change the small subscript numbers inside a compound; you can only balance the equation by adding large numbers (coefficients) in front of the whole compound.