Chemistry 1. Atomic Structure & The Periodic Table

What is the relative charge of a proton?

$+1$

What is the relative mass of a neutron?

1

What is the relative charge of an electron?

$-1$

Where is the majority of the mass of an atom concentrated?

In the nucleus.

What does the 'atomic number' of an element represent?

The number of protons in the nucleus.

Define the term 'mass number'.

The total number of protons and neutrons in an atom.

Definition: Isotopes

Atoms of the same element with the same number of protons but a different number of neutrons.

What is the approximate radius of an atom?

$0.1\text{ nm}$ (or $1 \times 10^{-10}\text{ m}$).

How does the radius of a nucleus compare to the radius of the whole atom?

It is less than $\frac{1}{10\,000}$ of the atom's radius (about $1 \times 10^{-14}\text{ m}$).

Why do atoms have no overall electrical charge?

They have an equal number of protons and electrons.

Term: Relative atomic mass ($A_{r}$)

An average value that takes into account the abundance of the isotopes of an element.

What was Dalton's 1803 model of the atom?

Atoms are tiny, indivisible spheres.

Which subatomic particle did J.J. Thomson discover in 1897?

The electron.

Describe the 'Plum Pudding' model of the atom.

A ball of positive charge with negative electrons embedded in it.

What were the three key observations from Rutherford's Alpha Scattering Experiment?

Most particles passed through, some were deflected, and a few bounced back.

What did the observation that most alpha particles passed through gold foil suggest about atoms?

Atoms are mostly empty space.

What did the deflection of alpha particles in Rutherford's experiment prove?

The nucleus is positively charged.

What did the fact that some alpha particles bounced back prove about an atom's mass?

The mass is concentrated in a tiny central nucleus.

What was Niels Bohr's 1913 contribution to the atomic model?

He suggested electrons orbit the nucleus at specific distances called shells.

Which scientist provided experimental evidence for the existence of neutrons in the nucleus?

James Chadwick (in 1932).

In what order were the three main subatomic particles discovered?

Electrons, then protons, then neutrons.

How many electrons can the first energy level (innermost shell) hold at maximum?

2

What is the maximum number of electrons the second energy level can hold?

8

What is the electronic structure of Sodium (atomic number 11)?

2, 8, 1

How are elements arranged in the modern periodic table?

In order of increasing atomic number.

Why is the table called the 'periodic' table?

Similar properties occur at regular intervals (periods).

How did early scientists attempt to classify elements before the discovery of subatomic particles?

By arranging them in order of their atomic weights.

What did Mendeleev do differently with his periodic table compared to previous versions?

He left gaps for undiscovered elements and swapped the order to match properties.

Why did Mendeleev's periodic table eventually become accepted by the scientific community?

Elements were discovered that filled his gaps and matched his predicted properties.

What determines the chemical properties of an element?

The number of electrons in its outer shell.

Elements that react to form positive ions are called _.

Metals

Where are non-metals located on the periodic table?

Towards the top and right.

What is the name for the elements in Group 0?

Noble gases.

Why are Group 0 elements unreactive?

They have a stable, full outer shell of electrons.

What is the trend for boiling points in Group 0 as you move down the group?

Boiling points increase.

How many electrons do most noble gases have in their outer shell (excluding Helium)?

8

What is the common name for elements in Group 1?

Alkali metals.

What is the trend for reactivity in Group 1 as you go down the group?

Reactivity increases.

Why does Group 1 reactivity increase down the group?

The outer electron is further from the nucleus, meaning less attraction and easier loss.

Which Group 1 metal produces a lilac flame when reacting with water?

Potassium ($K$).

What are the common products when an alkali metal reacts with water?

A metal hydroxide and hydrogen gas.

What is the name for elements in Group 7?

Halogens.

What type of molecules do Group 7 elements form?

Diatomic molecules (pairs of atoms, e.g., $Cl_{2}$).

What is the trend for reactivity in Group 7 as you go down the group?

Reactivity decreases.

Why does Group 7 reactivity decrease down the group?

Increased distance and shielding make it harder to attract an incoming electron.

In Group 7, how do melting and boiling points change down the group?

They increase.

A more reactive halogen can _ a less reactive halogen from an aqueous solution of its salt.

Displace

Where are transition metals found in the periodic table?

In the central block between Group 2 and Group 3.

Compared to Group 1 metals, how do transition metals differ in density?

Transition metals are much denser.

How do the melting points of transition metals generally compare to Group 1 metals?

Transition metals have much higher melting points.

What is a characteristic property of transition metal compounds?

They are often coloured.

In terms of chemical use, what do transition metals often act as?

Catalysts.

What distinguishes transition metals from Group 1 in terms of ion formation?

Transition metals can form ions with different charges (e.g., $Fe^{2+}$ and $Fe^{3+}$).

What is the atomic number of an isotope of Gallium with 31 protons and 38 neutrons?

31

What is the mass number of an atom with 31 protons and 38 neutrons?

69

Formula: Relative atomic mass ($A_{r}$)

$A_{r} = \frac{\sum (\text{isotope mass} \times \text{abundance})}{\sum \text{abundance (usually 100)}}$

Calculate $A_{r}$ for Gallium if 60% is Gallium-69 and 40% is Gallium-71.

$69.8$

Why did the discovery of isotopes explain why some atomic weights were not whole numbers?

Because the observed weight is an average of different isotopes with different masses.

What is the electronic structure of the chloride ion ($Cl^{-}$)?

2, 8, 8

Which Group 0 element has the same electronic structure as the chloride ion?

Argon ($Ar$).

What observation is made when Potassium reacts with water that isn't seen with Lithium?

The production of a lilac flame.

In the context of Group 1 trends, define 'shielding'.

Internal electron shells blocking the nuclear attraction on the outer electron.

How many outer shell electrons does Tennessine (atomic number 117) have?

7 (it is in Group 7).

What determines which element an atom belongs to?

The number of protons (atomic number).

Explain why metals have high melting points using their bonding structure.

Strong metallic bonds between delocalised electrons and positive ions require much energy to break.

How many protons, neutrons, and electrons are in ${}_{11}^{23}Na$?

Protons: 11, Neutrons: 12, Electrons: 11.

What is the mass of an electron relative to a proton?

Approximately $\frac{1}{2000}$.

What provides the evidence for the modern model of the nuclear atom with shells?

The arrangement of elements in the modern periodic table.

What did Rutherford call the tiny, positively charged centre of the atom?

The nucleus.

What did the Plum Pudding model suggest about the distribution of mass in an atom?

It suggested mass was evenly distributed throughout the atom.

How many electrons does an atom of Neon (atomic number 10) have in its outer shell?

8

Why are elements in the same group of the periodic table chemically similar?

They have the same number of electrons in their outer shell.

What is the charge of a Magnesium ion?

$Mg^{2+}$

Which group contains elements that are all diatomic non-metals at room temperature?

Group 7 (Halogens).

What happens to the number of electron shells as you move down any group?

The number of electron shells increases.

Predict the reactivity of Rubidium compared to Potassium.

Rubidium is more reactive (it is lower in Group 1).

What is the electronic structure of Argon?

2, 8, 8

True or False: Electrons were discovered before protons.

TRUE

In ${}_{Z}^{A}X$ notation, what does 'A' represent?

The Mass Number.

What is the maximum number of electrons in the third shell for the first 20 elements?

8

How did knowledge of isotopes help explain Mendeleev's table order?

It showed that ordering by atomic weight was sometimes incorrect compared to atomic number.

Which particles were the last to be discovered as part of the atom's structure?

Neutrons.

What colour precipitate is formed when Silver Nitrate and Nitric Acid are added to a solution containing Chloride ions?

White precipitate.

What is the name of the instrumental method used to identify metal ions and their concentrations via line spectra?

Flame emission spectroscopy.

Why should the starting line in chromatography be drawn in pencil?

Pencil is insoluble and won't travel up the paper with the solvent.

In the Halide test, why is Nitric Acid added before Silver Nitrate?

To remove carbonate ions that might give a false-positive white precipitate.

What is the result of a 'squeaky pop' test?

The presence of Hydrogen gas.

Predict the state of Fluorine at room temperature.

Gas.

Predict the state of Iodine at room temperature.

Solid.

What happens to the density of Noble Gases as you go down Group 0?

Density increases.

If an atom has 15 protons and 16 neutrons, what is its atomic number?

15

What is the mass of a Nitrogen atom with 7 protons and 8 neutrons?

15

Which group of metals are soft enough to be cut with a knife?

Group 1 (Alkali metals).

Why does the blue colour of Copper Nitrate solution fade during electrolysis?

Copper ions are discharged and removed from the solution.

What is the charge of an oxide ion?

$O^{2-}$

Identify the element: 2, 8, 2 electronic structure.

Magnesium ($Mg$).

Which halogen is a liquid at room temperature?

Bromine ($Br$).

What did the theoretical calculations of Bohr agree with?

Experimental observations of electron energy levels.

What type of bonds involve the sharing of electron pairs?

Covalent bonds.

What type of bond is formed when electrons are transferred from a metal to a non-metal?

Ionic bond.