chemistry - atomic structure and the periodic table

topic 1

What is an atom?

The smallest part of an element that can exist.

What is an element?

A substance made of only one type of atom.

What is a compound?

A substance formed when two or more elements are chemically bonded together.

How are compounds formed?

By chemical reactions involving the formation of bonds.

How can compounds be separated into elements?

By chemical reactions.

What are chemical symbols and formulae used for?

To represent elements and compounds.

What is a mixture?

A combination of two or more substances that are not chemically combined.

How can mixtures be separated?

Using physical methods such as filtration, crystallisation, simple distillation, fractional distillation, and chromatography.

What is the difference between a mixture and a compound?

Mixtures are not chemically combined and can be separated physically; compounds are chemically bonded.

Describe a practical application of chromatography.

Identifying substances in inks or food colourings.

What did John Dalton suggest about atoms?

That all matter is made of atoms which are indivisible and unique to each element.

What did the plum pudding model propose?

Atoms are spheres of positive charge with electrons embedded in them.

How did Rutherford's experiment change the atomic model?

His alpha particle scattering experiment led to the nuclear model: a small, dense, positive nucleus surrounded by electrons.

What did Bohr propose?

Electrons orbit the nucleus in fixed shells.

What did later experiments show about the nucleus?

That it contains protons and neutrons.

What is the relative charge of a proton?

+1

What is the relative charge of a neutron?

0

What is the relative charge of an electron?

-1

What is the radius of an atom?

Approximately 0.1 nm (1 × 10^-10 m).

What is the radius of the nucleus?

Less than 1/10,000 of the radius of the atom.

Where is most of the atom's mass concentrated?

In the nucleus.

What is the relative mass of a proton and neutron?

1 for both.

What is the relative mass of an electron?

Very small (1/1836 or negligible).

How is relative atomic mass (Ar) calculated?

Ar = (sum of (isotope abundance × isotope mass number)) / 100

How are electrons arranged in shells?

2 in the first shell, 8 in the second, 8 in the third (for first 20 elements).

What determines the way an element reacts?

The number of electrons in the outer shell.

How are elements arranged in the modern periodic table?

In order of increasing atomic number.

What do the rows and columns in the periodic table represent?

Rows = periods (number of shells); Columns = groups (number of outer electrons).

Why was the early periodic table incomplete?

Some elements were unknown and it was ordered by atomic mass.

How did Mendeleev improve the periodic table?

He left gaps and changed the order based on properties.

What are the properties of Group 0 elements?

Unreactive, colourless gases with full outer shells.

What is the trend in boiling points of noble gases?

Boiling point increases with increasing relative atomic mass.

What happens when alkali metals react with water?

They produce a metal hydroxide and hydrogen gas.

What are the physical properties of alkali metals?

Soft, low melting points, low density.

What is the trend in reactivity down Group 1?

Reactivity increases down the group.

What are the physical states of halogens at room temperature?

Fluorine (gas), chlorine (gas), bromine (liquid), iodine (solid).

What is the trend in reactivity in Group 7?

Reactivity decreases down the group.

What is a displacement reaction in Group 7?

A more reactive halogen displaces a less reactive halogen from its compound.

Where are transition metals found in the periodic table?

In the centre, between Groups 2 and 3.

Give 3 properties of transition metals.

High melting points, form coloured compounds, act as catalysts.

How do transition metals compare to Group 1 metals?

Harder, denser, less reactive, higher melting points.

What distinguishes metals from non-metals?

Metals form positive ions and conduct electricity; non-metals form negative ions or share electrons and are insulators.

What determines whether an element forms a positive or negative ion?

Position in the periodic table and number of outer electrons.

List some physical properties of metals.

Malleable, ductile, good conductors of heat and electricity, high melting and boiling points.

Why are metals good conductors?

Because of delocalised electrons that carry energy and charge.