Atomic theory and bonding

Question 1

What is a nanometre?

Answer 1

one billionth of a metre (10^-9) m

Question 2

Bottom up method

Answer 2

Using specially designed molecules or atoms in chemical reactions to gradually build up the new nanoparticles from the smaller atoms or molecular units.

Question 3

Top down method

Answer 3

Uses the larger bulk material as the starting material/ The bulk material is broken down into nanoparticles by mechanical or chemical means.

Question 4

What is the size range for nanoparticles?

Answer 4

1 to 100 nm

Question 5

What did Dalton’s atomic theory propose?

Answer 5

• All matter is composed of tiny indivisible particles called atoms
• All atoms of the same element are identical in mass and properties
• Compounds containing atoms of different elements combine in whole number ratios
• Atoms are neither created nor destroyed in chemical reactions
• Most stable compounds of two elements contains atoms in 1:1 ratio

Question 6

What has know been known about atoms compared to Dalton’s theory?

Answer 6

Scientists now know that atoms are not indivisible or indestructible and are made up of even smaller subatomic particles.

Question 7

What is an element?

Answer 7

A substance composed of one type of atom only, with the same atomic number.

Question 8

What is a compound?

Answer 8

Two or more different types of atoms chemically bonded together in a fixed ratio.

Question 9

Why are atoms neutral?

Answer 9

Number of positive charges is equal to number of negative charges.

Question 10

What is an isotope?

Answer 10

Atoms with the same atomic number (number of protons) but different mass numbers (number of neutrons).

Question 11

What did J J Thompson propose?

Answer 11

He identified the electron showing atoms were not indivisible. He proposed atoms consisted of a soft positively charged sphere into which negatively charged electrons were embedded. plum pudding model

Question 12

What did Rutherford propose?

Answer 12

He fired alpha particles, heavy positive at very thin gold foil indicating a very dense positively charged core, the nuclei, with most of the atom being empty space. He then proposed the mass and positive change is concentrated in the centre, the nucleus. Negatively charged electrons occupy space around it, taking up most of the volume of the atom.

Question 13

What did the Bohr model propose?

Answer 13

• Electrons revolve around the nucleus in fixed, circular orbits.
• The electron’s orbits correspond to specific energy levels of higher energy.
• Electrons can only occupy fixed energy levels and cannot sexist between two energy levels.
• Orbits of larger radii correspond to energy levels of higher energy.

Question 14

How did Bohr come to this conclusion?

Answer 14

He put an electric current through a sample of hydrogen. Some electrons in their ground state, electrons in their lowest energy level, absorbed some of this energy and moved to an excited state, higher energy level. In the excited state the electrons are unstable and quickly returned to their ground state, emitting the energy absorbed in the form of electromagnetic radiation. If this energy is equivalent to the energy of light within the visible region of the spectrum we see this as coloured light. If this light is passed through a prism it is split into into component wavelengths, seen as coloured lines on a black background or emission spectrum.

Question 15

What is the ground state?

Answer 15

When the electron is in the lowest possible energy shell, lowest energy state of the atom.

Question 16

What are the two exceptions to the normal way sub shells are filled?

Answer 16

Chromium and Copper

Question 17

What is core charge?

Answer 17

The measure of the electrostatic attraction felt by valence electrons towards the nucleus, taking into account any inner shell electrons.

Question 18

What is core charge equal to?

Answer 18

Atomic number minus number of full inner shell electrons.

Question 19

What is atomic radius?

Answer 19

Distance from nucleus to valence shell

Question 20

What happens to atomic radium down a group?

Answer 20

Down a group core charge stays constant as number of energy levels (shells increases). Valence electrons are less strongly attracted to the nucleus.

Question 21

What happens to atomic radium across a period?

Answer 21

Decreases. As you move across a period he number of occupied shells in the atoms remains constant but the core charge increases. the valence electrons become more strong attached to the nucleus so atomic radii decreases across a period.

Question 22

What is the key feature that changes across a period bringing about these trends?

Answer 22

the number of protons in the nucleus and core charge.

Question 23

What is the changing factor that explains trends down a group?

Answer 23

The increase in the number of energy levels is what causes the trends down a group. As you go down a group you add a shell, valence electrons get further from the nucleus, more easily lost and reactivity increases.

Question 24

What is electronegativity?

Answer 24

The ability of an atom to attract electrons towards itself.

Question 25

What happens to electronegativity down a group?

Answer 25

The core charge stays constant and the number of shells increases down a group. Therefore valence electrons are less strong attracted to the nucleus as they are further from the nucleus.

Question 26

What happens to electronegativity across a period?

Answer 26

The number of occupied shells in the atoms remains constant but the core charge increases across a period. Therefore the valence electrons become more strong attracted to the nucleus.

Question 27

What is ionisation energy?

Answer 27

The energy required to remove an electron from an atom

Question 28

What happens to ionisation energy across a period?

Answer 28

As you go across a period the elements have the same number of shells but the number of protons and core charge increases. This strengthens the electrostatic attraction between the nucleus and valence electrons so the atom attracts it valence electrons more strongly as they are harder to remove.

Question 29

Why is first ionisation energy lower down a group?

Answer 29

Core charge stays constant and number of shells increase down a group. The valence electrons are less attracted to the nucleus as they are further from the nucleus. The energy required to overcome the attraction between the nucleus and the valence electron is less and the first ionisation energy decrease down a group.`

Question 30

What happens to reactivity of metals down a group?

Answer 30

Increases as it is easier from a metal with a greater number to shells to lose electrons.

Question 31

What happens to reactivity of metals across a period?

Answer 31

Decreases across a period as the increasing core charge makes it more difficult for a meal to lose electrons.