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Democritus (300 B.C.)
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First person to conceive the idea of tiny, indivisible particles called atoms
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John Dalton (1805) - The billiard ball model
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Pure substances are made up of atoms
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Atoms of the same element are exactly alike
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Atoms cannot be created, destroyed, or divided into smaller particles
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Compounds are formed by joining 2 or more elements
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William Crookes (1875) - Discovery of the electron
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Created an electric discharge tube (a cathode ray tube) with a screen and magnet
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Discovered the bar magnet could deflect/move the cathode rays (they have a charge)
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If he added a paddle wheel inside the tube, it moved (the rays had mass)
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J.J. Thomson (1897) - The raisin bun model
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Using Crooke's cathode ray tube, determined rays were made up of negatively charged particles called electrons
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Electrons were 2000x lighter than hydrogen, the lightest known element
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Ernest Rutherford (1903) - The beehive model
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Conducted the gold foil experiment; if the atom was like Thomson proposed, any alpha particles sent through it would pass straight through
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Most of the particles went through, but some were scattered
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Determined that atoms were mostly empty space, with a small, dense, positively charged nucleus in the centre with e¯ scattered around it
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1932 - determined with James Chadwick that the mass of the nucleus did not equal the mass of the protons only, i.e. electrically neutral neutrons
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Niels Bohr (1913) - The planetary model
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Proposed that electrons are not allowed to orbit anywhere, but rather they occupy certain defined (fixed) orbits
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Based off experiments with hydrogen atoms and spectroscopes
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Electrons can jump to higher orbits when they are given energy in quantized amounts (no partial amounts), usually in the form of photons (light particles)
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Louis de Broglie (1924) proposed that if light waves properties of particles, then particles can have properties of waves
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Erwin Schrodinger (1933) realized that a wave theory and mathematical equations were needed to explain atoms with more than 2 e_
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Schrodinger's Wave Function
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Contains 3 variables called quantum numbers (n, l
n, ml) to help determine a region in space where the electron spends 90% of its time (the atomic orbital) |
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A fourth number (m
s) was added so that all characteristics of atoms could be explained |
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Heisenberg's Uncertainty Principle: it is impossible to know both the exact location and speed of an e_ at a given time
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Valence Bond Theory: atomic orbitals of one atom can overlap with atomic orbitals of another atom to share a common region of space
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Molecular Orbital Theory: when orbitals overlap, they combine to form new orbitals called molecular orbitals (hybridization); the greater the overlap, the more stable the bond
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Double/Triple Bonds: Sigma (σ) bonds (end-to-end overlap of orbitals) and pi (π) bonds ("sideways" orbitals—usually p orbitals—overlap above and below the plane of the bond)
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Single bond = 1 σ bond; Double bond = 1 σ bond + 1 π bond; Triple bond = 1 σ bond + 2 π bonds
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Quantum number
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Symbol
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Meaning
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Possibilities
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Principal quantum number
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n
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Energy level
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n Є ℕ (any whole number > 0)
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Secondary quantum number
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l
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Shape of orbital
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0 ≤ l ≤ n - 1
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Magnetic quantum number
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m
l |
Direction/orientation
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-l ≤ -m
l ≤ l |
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Spin quantum number
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m
s |
Spin
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±
1/2 |
l)
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Value of l
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Symbol
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Shape
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# of suborbitals (m
l) |
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0
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s (sharp)
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1 (m
l = 0) |
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1
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p (principal)
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3 (m
l = -1, 0, 1) |
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2
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d (diffuse)
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5 (m
l = -2, -1, 0, 1, 2) |
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3
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f (fundamental)
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7 (m
l = -3, -2, -1, 0, 1, 2, 3) |
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VSEPR: Valence Shell Electron Pair Repulsion
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Helps determine the structure around an atom by minimizing the repulsive force between e¯ pairs
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Bonded and lone pair e¯ position themselves as far away as possible from each other
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Lone pairs of e¯ on a central atom repels a little more than bonding pairs; they push the bonding pairs closer together
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# of e¯ groups
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e¯ configuration
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AXE formula
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Molecular shape
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2
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Linear
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AX
2 |
Linear
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3
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Trigonal planar
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AX
3 |
Trigonal planar
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AX
2E |
Bent
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||
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4
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Tetrahedral
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AX
4 |
Tetrahedral
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AX
3E |
Trigonal pyramidal
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||
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AX
2E2 |
Bent
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5
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Trigonal bipyramidal
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AX
5 |
Trigonal bipyramidal
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AX
4E |
See-saw
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AX
3E2 |
T-shape
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AX
2E3 |
Linear
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6
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Octahedral
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AX
6 |
Octahedral
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AX
5E |
Square pyramidal
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||
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AX
4E2 |
Square planar
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Bond Polarity: the even/uneven distribution of e¯ across one bond (can be single/double/triple); determined by ΔEN (difference in electronegativity)
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Molecular Polarity: the even/uneven distribution of e¯ across an entire molecule; determine many properties of the substance
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3 important factors to molecular polarity: presence/absence of polar bonds, shape of the molecule, and presence/absence of lone e¯ pairs
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Solids in which positive and negative ions are arranged in a crystal lattice
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Boiling/melting point
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High
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Malleability
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Brittle
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Conductivity
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Poor as solid, high as solution
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Solubility in water
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Very soluble
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Hardness
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Very hard (very scratch-resistant)
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Types of forces acting on molecule
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Ionic bonds
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3PO4 (potassium phosphate), CuSO4 (copper (II) sulfate)
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Solids composed of individual molecules held together by intermolecular forces (IMFs); "neutral" molecules that form complex crystal lattice in solid state
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Boiling/melting point
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Vary widely
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Malleability
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Ductile (very flexible)
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Conductivity
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High as a solid
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Solubility in water
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Slightly soluble
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Hardness
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Varied
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Types of forces acting on molecule
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Metallic bonds
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Ionic Bond: Highly electropositive ion (cation) gives up extra e¯ and gives them to highly electronegative ion (anion), then bond through very strong electrostatic attraction between the two ions, creating an ionic crystal structure
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Metallic Bond: Many metal atoms shed a "sea" of e¯ that engulf the metal ions (e¯ are delocalized); pulled from all directions, the metal ions can barely move and pack tightly together in crystalline structures
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Solids composed of individual molecules held together by intermolecular forces (IMFs); "neutral" molecules that form complex crystal lattice in solid state
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Boiling/melting point
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Low
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Malleability
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N/A
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Conductivity
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Poor as solids
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Solubility in water
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Varied
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Hardness
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Soft (easy to scratch)
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Types of forces acting on molecule
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IMFs - weaker than ionic/metallic bonds
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2(s) (iodine), At2(s) (astatine)
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Solids in which the atoms form covalent bonds in an interwoven network; most contain C or Si atoms
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Boiling/melting point
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Very high
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Malleability
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N/A
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Conductivity
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Poor as solids
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Solubility in water
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Varied
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Hardness
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Extreme hardness or softness
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Types of forces acting on molecule
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Covalent bonds (strength increases with more bonds); sometimes IMFs (usually LDF)
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