Presentation about atom structure and chemical bond

1. 6. Atoms & chemical bond
1. Classical atom models
2. Böhr model
3. Electron structures
4. Periodic system
5. Chemical bonds

2. 1. Chemistry
Science which studies
composition, properties
and transformations of
mixtures and chemical
substances

3. 1. Dalton model
Matter consists of indivisible
particles, called atoms
Elements are substances
which consist of the same
type of atoms
Atoms are combined to
produce molecules according
to ratios of integer numbers

4. 1. Thomson model
1897: Electron discovery (J.J.
Thomson)
1904: Thomson model (plum
pudding)

5. 1. Rutherford model
1911: Gold foil experiment: scattering of α particles
1911: Rutherford model: nucleus and electon shell

6. 2. Atom spectra
Range of frequencies
which are emitted by an
element
Continuous & discrete
spectra
http://chemistry.bd.psu.edu/jircitano/periodic4.html

7. 3. Atom spectra
• Fingerprint of elements
• More transitions as the number of protons increase

8. 2. Plank hypothesis
1900: Planck hypothesis
Particles can only have discrete
quanta of energy which are
proportional to frequency
E = n. hν
h = 6,63.10-34
J.s

9. 2. Böhr model
1913: Niels Böhr described the first
quantum model
Simplest model of an atom: just few
allowed orbits
Prediction of lines in hydrogen
spectrum

10. 3. Electron structures
Levels and sublevels of energy
Level given by a number
(electron shells)
Sublevel given by a letter
Distribution of electrons,
which gives the number of
electrons and their energy
Aufbau law : diagonals
Pauli exclusion law
Valence shell: octet rule

11. 4. History of periodic system
1817: Döbereiner triads
Li/Na /K; Ca/Sr/Ba; Cl /Br /I
1864: Newlands octaves
Li, Be, B, C, N, O, F, Na...
1869: Mendeleiev periodic table

12. 4. Mendeleiev periodic table
Table
Atomic mass sequence
Gaps and irregularities

13. 4. Electron structure & periodic system

14. 4. Electron structure & periodic system
Atomic number
7 Periods (electron shells)
18 groups same electron
structure in valence shell
(same chemical properties)
Electronic structure
Metals, non metals, noble gases

15. 5. Chemical bond
Electrostatic attraction
between nuclei and
electron shells
Electric repulsión between
electron shells
Chemical bond: minimal
potential energy
Interaction between 2 or
more atoms

16. 5. Ionic bond
Octet rule (Lewis, 1916): Lewis
structures
Metal & non metal combination
Electron ransfer from metal to
non metal
Ions formation
Electrostatic atraction

17. 5. Covalent bond
Non metales combination
Sharing a pair of electrons
Lewis structures
Homoatomic molecules
Bonding (shared) pairs
Non-bonding (unshared pairs)
Multiple bonds: double and triple

18. 10. Metallic bond
All the valence electrons are shared
Sea of electrons /gas of electrons
Free /random motion of electrons