Early Ideas of the Atom

Transcription

1 Atoms the smallest particle of an element that retains its identity in a chemical reaction. - electrically neutral - spherical - positively charged nucleus surrounded by one or more negatively charged electrons

2 Early Ideas of the Atom Democritus: believed that atoms were indivisible and indestructible Dalton: first organized atomic theory based on the scientific method.

3 Experiments Thomson: discovered the electron using cathode ray tubes. Created the plumpudding model. Millikan: calculated the mass of the electron using the oil droplet experiment. Rutherford: discovered the nucleus using the gold foil experiment. Disproved the plum-pudding model.

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6 Honors Chemistry 2.A Electrons in the Atom

7 The Bohr Model An electron is found only in specific circular paths, or orbits, around the nucleus Each possible electron orbit in Bohr s model has a fixed energy The fixed energies an electron can have are called energy levels.

8 an electron can jump from one energy level to another the electrons in an atom cannot be between energy levels an electron must gain or lose energy to move from one energy level to another (quantum) the higher an electron is on the energy ladder, the farther it is from the nucleus.

9 The Quantum Mechanical Model the quantum mechanical model does not involve an exact path the electron takes around the nucleus determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus based on probability

10 Atomic Orbitals A region of space in which there is a high probability of finding an electron. Solving Schrodinger s equation gives the energies an electron can have The energy levels are labeled by quantum numbers (n) Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

11 n=1 has 1 sublevel (1s) n=2 has 2 sublevels (1s 2p) n=3 has 3 sublevels (1s 2p 3d) n=4 has 4 sublevels (1s 2p 3d 4f)

12 Electron Configurations Electrons and the nucleus interact to make the MOST STABLE arrangement Electron Configurations are the ways in which electrons are arranged in different orbitals around the nucleus The following rules tell you how to find the electron configurations of atoms...

13 The Aufbau Principle Each box represents an orbital The s sublevel is always the

14 Pauli Exclusion Principle and Hund s Rule an atomic orbital may describe at most two electrons, each with opposite spin direction electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible

15 The principle quantum energy level only holds that many sub-levels. Principal Energy Level # of sub-levels sub-levels n=1 1 1s n=2 2 2s 2p n=3 3 3s 3p 3d n=4 4 4s 4p 4d 4f

16 The number of electrons in each sub-level. sub-level # of electrons in each sub-level s 2 p 6 d 10 f 14

17 Maximum number of electrons in each energy level. Principal Energy Level (n) sub-levels electrons total number of electrons 1 1s s 2p s 3p 3d s 4p 4d 4f

18 The orbitals in each sub-level. sublevel # of electrons in each sublevel # of orbitals Names of each orbital s 2 1 s p 6 3 pz px py d 10 5 dz 2 dxz dyz dxy dx 2 -y 2 f 14 7 fz 3 fxz 2 fyz 2 fxyz fz(x 2 -y 2 ) f x ( x 2-3 y 2) f y (3 x 2- y 2)

19 Electron Configuration Rules 1.Identify how many electrons are in the atom. 2.There is a maximum of 2 electrons per orbital. Total electrons: s=2, p=6, d=10, f=14 3.Electrons do not pair up within an energy sub-level until each orbital already has 1 electron. 4.Place electrons in the orbitals (lowest energy first) until the superscripts add up to the total number of electrons.

20 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 14...

21 Periodic Table Shortcut PERIOD # = # of shells / energy levels

22 Electron Configurations of Ions Na: Na + :

23 Exceptional EC s Chromium: Cr What we would predict: What it actually is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 The 3d suborbital is more stable when either half filled OR completely filled. Copper: Cu What we would predict: What it actually is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 These transfers lower the overall energy.

24 Valence Electrons The electrons in the highest occupied energy level of an atom Using electron configuration: add the s electrons and the p electrons only example: P: 1s 2 2s 2 2p 6 3s 2 3p 3 2+3= 5 valence e- Using group number: GROUP # = # valence e- These are usually the only electrons involved in chemical bonds

25 The Periodic Table of Elements Periods (row) & Groups (columns) Metals: good conductors (heat & electricity), ductile, malleable, shiny Metalloids: properties are similar to, and in between, metals and nonmetals Nonmetals: poor conductors & brittle. Physical properties differ between nonmetals (hard to generalize).

26 Trends in the Periodic Table: Atomic Size

27 Trends in the Periodic Table: Ionization Energy Ionization Energy: the energy required to remove an electron from an atom and overcome the electron+proton attraction. Related to ionic charge.

28 Trends in the Periodic Table: Ionic Size Cations (+) -> lost e - -> smaller Anions (-) -> gained e - -> larger

29 Trends in the Periodic Table: Electronegativity Electronegativity: the ability of an atom to attract electrons when the element is part of a compound. Can be used to predict the type of bond that will form The most electronegative element is F