Atomic Structure Flashcards
What is a molecule?
A (small) number of atoms covalently bonded together
What is an ion?
An atom (or group of atoms) that has gained or lost electrons
What is an element?
A substance that contains only one type of atom
What is a compound?
A compound contains two or more different types of atoms chemically bonded together (ionic or covalent)
What is a mixture?
A mixture contains two or more substances (elements or compounds) that are not chemically bonded together
Define Relative Atomic Mass
The weighted average mass of an atom of an element (including all isotopes) relative to 1/12 of an atom of C-12
Define Relative Molecular Mass
The mass of a molecule relative to 1/12 of an atom of C-12
What is a mole?
Amount of substance containing Avogadro’s constant (6.022x10^23) number of particles
Define Molecular Formulae
The actual number of atoms of each element in a substance/compound
Define Empirical Formulae
The simplest whole number ratio of an atom within a substance
Define First Ionisation Energy
The amount of energy required to remove one mole of electrons from one mole of gaseous atoms to form gaseous ions
X(g) —> X+(g) + e-
Define Second Ionisation Energy
The amount of energy required to remove one mole of electrons from one mole of a 1+ gaseous ion to form one mole of 2+ gaseous ions
X+(g) —> X2+(g) + e-
What are the 3 factors that affect ionisation energy?
Shielding (amount of shells)
Nuclear Charge
Atomic Radius
What is the trend of ionisation energies across a period
Ionisation energy increases because:
- more protons in nucleus (nuclear charge increases)
- atomic radius decreases (outer e- closer to positive nucleus)
- no additional shielding
What is the trend of ionisation energies down a group?
Ionisation energy decreases because:
- atomic radius increases (outer e- further away from positive nucleus)
- more shielding
- nuclear charge has no effect
Explain the deviation from the trend between beryllium + boron (also applies to Mg and Al)
Boron has a lower IE than Beryllium because
- Boron atom has more shielding therefore outer e- is further from the positive nucleus
- Boron’s outer e- is in a higher energy sub shell (p) than Beryllium’s outer electron which is in the s sub shell
Explain the deviation from the trend between nitrogen + oxygen (also applies to P and S)
Oxygen has a lower IE than Nitrogen because:
- e- paired in 2nd p orbital
- paired e- repel
- therefore outer e- more easily lost
What is an isotope?
Isotopes are atoms of the same element with a different number of neutrons
Define ‘mass number’ of an atom
The total number of protons and neutrons in the nucleus
