CHEM UNIT 1 HIGHERs

What does the periodic table arrange elements by?

Increasing atomic number.

What are groups in the periodic table?

Vertical columns containing elements with similar chemical properties due to a common number of outer shell electrons.

What are periods in the periodic table?

Rows of elements arranged by increasing atomic number, showing a transition from metallic to non-metallic characteristics.

List the categories of the first 20 elements in the periodic table.

Metallic, covalent molecular, covalent network, and monatomic (noble gases).

What is the covalent radius?

A measure of the size of an atom.

What is the first ionisation energy?

The energy required to remove one mole of electrons from one mole of gaseous atoms.

What factors influence ionisation energies?

Atomic size, nuclear charge, and the screening effect due to inner shell electrons.

What is electronegativity?

A measure of the attraction an atom has for the electrons in a bond.

How does electronegativity trend across periods and down groups?

It can be rationalised in terms of covalent radius, nuclear charge, and the screening effect.

What is a covalent bond?

A bond formed when atoms share pairs of electrons.

What is a polar covalent bond?

A bond formed when the attraction for the pair of bonding electrons is different between atoms.

What are ionic bonds?

Electrostatic attractions between positive and negative ions.

What is the difference between pure covalent and ionic bonding?

Pure covalent bonding involves equal sharing of electrons, while ionic bonding involves complete transfer of electrons.

What are van der Waals forces?

Intermolecular forces acting between molecules, including London dispersion forces and permanent dipole interactions.

What are London dispersion forces?

Weak forces of attraction that can operate between all atoms and molecules, caused by temporary dipoles.

What defines a polar molecule?

A molecule that has a permanent dipole due to the spatial arrangement of polar covalent bonds.

What are hydrogen bonds?

Electrostatic forces of attraction between molecules containing highly polar bonds (e.g., H bonded to F, O, or N).

How do hydrogen bonds compare in strength to other interactions?

Stronger than permanent dipole interactions but weaker than covalent bonds.

What physical properties are influenced by intermolecular forces?

Melting points, boiling points, viscosity, and solubility.

Why do polar substances have higher boiling points than non-polar substances?

Due to stronger intermolecular forces such as hydrogen bonding.

What is the significance of hydrogen bonding in ice?

It results in an expanded structure, making ice less dense than water.

What determines the solubility of ionic and polar compounds?

Their tendency to dissolve in polar solvents like water and be insoluble in non-polar solvents.

What features indicate potential hydrogen bonding in molecules?

Presence of O-H or N-H bonds.