Mass # atomic # protons + neutrons = protons = Atomic Symbols.
AS Chemistry – Atomic structure and bonding. Sub-atomic particles Protons – mass 1; charge +1...
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Transcript of AS Chemistry – Atomic structure and bonding. Sub-atomic particles Protons – mass 1; charge +1...
Sub-atomic particles
• Protons – mass 1; charge +1
• Electrons – mass 1/1840; charge –1
• Neutrons – mass 1; charge 0
• Atomic number – number of protons in nucleus
• Mass number – protons + neutrons in nucleus
• Electrons – (atomic number – charge)
Relative masses
• Mass relative to 1/12th mass of 1 atom carbon-12
• Relative atomic mass: weighted mean of relative isotopic masses
• Relative molecular mass:sum of relative atomic mass in molecular formula
• Empirical – simplest ratio
• Molecular – atoms in a molecule
Mass spectroscopy
• Vaporisation
• Ionisation – E (g) + e- (high energy) E+ (g) + 2e-
• Acceleration – from +; through – grid
• Deflection – magnetic field
• Detection
How many protons, neutrons and electrons
•24He
2 protons, 2 neutrons, 2 electrons•
2145Sc
21, 24, 21•
1735Cl
17, 18, 17•
1737Cl-
17,20,18
Ionisation energy & electron affinity
• 1st ionisation energy: E (g) E+ (g) + e-
• 2nd ionisation energy: E+ (g) E2+ (g) + e-
• 1st electron affinity: E (g) + e- E- (g)
• 2nd electron affinity: E- (g) + e- E2- (g)
Electron configuration• Sequential ionisation energies: major quantum
shells
0
2 0
4 0
6 0
8 0
1 00
1 2 0
1 4 0
1 6 0
1 8 0
2 00
1 2 3 4 5 6 7 8 9 10 11 12
• Sodium 2, 8, 1
Electron configuration• 1st ionisation energies: quantum sub-shells
0
5 0
1 00
1 5 0
2 00
2 5 0
H He Li Be B C N O F Ne Na
• Sodium 1s2 2s2 2p6 3s1
Write full electron configurations for:
•6C 1s22s22p2
•17Cl 1s22s22p63s23p5
•20Ca 1s22s22p63s23p64s2
•23V 1s22s22p63s23p64s23d3
•29Cu 1s22s22p63s23p64s13d10
Bonding
• Ionic/electrovalentopposite charges attracthigh m.p./b.p. – a lot of energy needed
to overcome attractionsconducts as liquid/solution because ions
can move• Covalent
Shared electron pairs – one from each atom• Dative/coordinate covalent Shared electron pairs – both from same atom
Type of covalent bond
• Perpendicular overlap of orbitals:π bond
Limited rotation about π bond can result in cis-trans isomerism
Electron density map for hydrogen molecule
High concentration of negative charge between H nuclei.
This is strongly attracted by both nuclei so attractive interactions exceed repulsive ones
Bonding determines structure • Extensive bonding in all directions in
space results in giant structures• Metals and ionic compounds always
have giant structures • Most covalent compounds exist as
molecules but some have giant structures eg diamond and silica (SiO2)
• If no bonds are formed then the substance is a monatomic gas
Intermediate nature of bond• Electronegativity
Atoms at opposite end of bond have differentattraction for bond pair of electrons
More electronegative atom becomes slightly -ve
Hδ+-Clδ-
• Polarising
Small highly charged cations polarise anionstowards covalency
1+ 2+
Polar bonds and polar molecules
• Symmetrically arranged polar bonds produce a non-polar molecule
Cl
Cl
C
Cl
Cl
H
Cl
C
Cl
Cl
PolarNon-polar
Intermolecular forces
• Van der Waals
Moving electrons produce a temporary dipole
Temporary dipoles induce dipoles
Size of dipole proportional to number of electrons
Closer packing gives greater attraction
Intermolecular forces
• Permanent dipole
Polar molecules have stronger attractions
• Hydrogen bonds
Highly electronegative atom (& small)
Lone pair of electrons
Bonded to hydrogen
Hydrides
• General trend
Higher mass – larger van der Waals forces• Period 2
Van der Waals forces + hydrogen bonds
-40
-20
0
20
40
60
80
100
120
2 3 4 5
Giant covalent (network covalent)
• Lattice of atoms joined by covalent bonds
• Lots of energy required to separate covalently bonded atoms
• Insulator – electrons fixed
• Graphite: covalently bonded layers (σ bond) delocalised electrons between layers (π bond)
Simple molecular
• Strong covalent bonds between atoms
• Low melting & boiling point
Weak forces (van der Waals/permanent dipole/hydrogen bonds) between molecules
• Insulator – no charged particles available to move
Giant Ionic Lattice
• Oppositely charged ions
• Lots of energy required to overcome strong electrostatic attraction
• Insulator as solid – ions fixed
• Conducts as liquid/solution – ions able to flow
Molecular shape
• Valence Shell Electron Pair Repulsion Theory
• Electron pairs in outer shell of central atom as far apart as possible in order to minimise repulsion
• Include bonded and non-bonded (lone) pairs