MODELS OF THE ATOM

MODELS OF THE ATOM

CHM 130

GCC

Review - Rounding• Round 399

Hopefully you said 400 not 4. What is wrong with 4???

The zeroes ARE important, they are place holders. 400 and 4 are NOT the same! If you had $400 in the bank but they said you had only $4 you’d be pissed off!

Round 2389 to 2 sig fig, now round to 1 sig fig

Answer: 2400 NOT 24 2000 NOT 2

1. An element is made of tiny, indestructible particles called atoms. (Not quite true – why?)

5.1 DALTON’S ATOMIC 5.1 DALTON’S ATOMIC THEORYTHEORY

2. All atoms of an element are identical and have the same properties. (Not quite true – why?)

3. Atoms of different elements combine to form compounds.

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4. Compounds contain atoms in small whole number ratios.

e.g. Each H2O molecule consists of one O and two H atoms, not ½ atoms or ¾ atoms.

5. Atoms of 2 or more elements can combine to form different compounds.

E.g. C and O may form CO or CO2

5.2 Thomson cathode ray experiment

Thompson “Plum Pudding Model” http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#

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•Atom is + charged

•e-’s are distributed throughout atoms like raisins in plum pudding

5.3 Rutherford’s Scattering Experiment http://www.mhhe.com/physsci/chemistry/animations/chang_2e/rutherfords_experiment.swf

Explanation of Scattering

Nuclear Model

1) The atom is mostly empty space with electrons moving around.

2) Each atom has a small, dense nucleus with the Protons & Neutrons.

Rutherford’s model

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nucleus (~10-13 cm diameter)

atom (~10-8 cm diameter)

If nucleus = size of a small marble, then atom is the size of Cardinal’s stadium!

Subatomic Particles

Particles

Symbol

Charge

Relative Mass (amu)

Electrons e- -1 1/1836

Protons p+ +1 1

Neutrons n 0 1

5.4 Atomic Notation

ATOMIC NUMBER

Every atom of an element has the same # of protons

The # of protons defines an element

Carbon atoms ALWAYS have 6 protons

Mass number

Mass number = # protons + neutronsSo how calculate # neutrons?

# neutrons = mass - # protons

Isotopes

Isotopes of an element have the same atomic number (# pro), but a different mass number (# neu).

Ex: carbon-12, carbon-13 and carbon-14

How many protons do the above have? Neutrons?

6

6, 7, 8

Ex. 1: Write the atomic notation for potassium-40.

How many neutrons are there?

______________40 – 19 = 21

K4019

Ex. 2: a. Write the atomic notation for bromine-81.

b. How many neutrons are there?

_________________81 - 35 = 46

rB8135

Isotope mass # # protons # neutrons # electrons

oxygen- 16

oxygen- 17

oxygen- 18

16 8 8 817 8 9 818 8 10 8

5.5 Atomic Mass

Masses of atoms are so small that we define the atomic mass unit (amu)

•Mass of proton & neutron 1 amu.•Mass of electron is basically zero amu

Atomic mass

Atomic Mass in the P. Table is the weighted average of all atoms for that element in the world, so that is why it is NOT a whole number.

Natural isotopes of carbon:carbon-12 (98.89%) carbon-13 (1.11%)

The atomic mass reported for carbon (12.01 amu) is closer to carbon-12 since it is most abundant isotope for C. (There is a ton more C-12 than C-13.)

Example: Use the Periodic Table to determine the most abundant isotope:

a. lithium-6 or lithium-7

b. chlorine-35 or chlorine-37

5.6 Light has two components: Wavelength () is the distance between peaks

Frequency () is the number of wave cycles per second. (like a beat)

• As wavelength , the frequency , and the energy

Which wave has higher energy? Lower frequency?

Radiant Spectrum:

5.7 In 1900, Max Planck proposed the controversial idea that energy was emitted in small bundles called quanta.

• a particle of light energy is called a photon

Ball loses potential energy continuously as it rolls down a ramp.

Ball loses potential energy in quantized amounts as it bounces down a stairway.

5.8 Bohr Model ~1913

Neils Bohr proposed that electrons orbit around the nucleus, occupying orbits with distinct energy levels. Electrons are quantized!

Bohr model of the atomBohr model of the atom

• The electrons orbit around the nucleus The electrons orbit around the nucleus kinda like planets orbit around the kinda like planets orbit around the sun but in 3D.sun but in 3D.

• These orbits are called energy levels These orbits are called energy levels or shells. or shells.

• Each orbit has a specific radius and Each orbit has a specific radius and energy, so a certain distance from the energy, so a certain distance from the nucleus. nucleus.

Bohr Model

The orbit closest to the nucleus is lowest in energy; the energy increases with distance from the nucleus. Proven by line spectra.

When the light from a heated element passes through a prism, a series of narrow lines is seen.

These lines are the emission line spectrum.

Atomic Fingerprints

Each element produces a different emission line spectrum, so its own unique color.

Each element has it’s own energy levels that are unique.

Bohr theory explains 3 lines in H2 spectra.

• Electrons gain energy from heat or electricity and jump to a higher energy level. These “excited” electrons ultimately lose energy and drop to lower energy levels, which causes light to be emitted.

5.9 Each Energy Level Can Be Subdivided Into Sublevels.

Levels: 1-7sublevels: s, p, d, and f.

Each Level Has n Sublevels:

1st level has One Sublevel 1s2nd level has Two Sublevels 2s 2p3rd level - Three Sublevels 3s 3p 3d4th level - Four Sublevels 4s 4p 4d 4f

This is depicted on next slide.

Orbitals are regions in space where there is a high probability of finding an electron.

– One orbital can hold a maximum of 2 electrons.

Each sublevel contains a specific number of orbitals.

s has 1 orbitalp has 3d has 5f has 7

Orbitals are boxes on next slide

5.10 Electron Configuration: Shorthand description of electrons by sublevel.

• Sublevels are filled in order of increasing energy.1s < 2s < 2p < 3s < 3p < 4s – You will do configurations for the 1st

20 elements. – Note the 3d sublevel is higher in energy

than the 4s which is why we fill 4s first

Writing electron configurations

1. # of electrons?2. Fill in sublevels to reach that #3. Use superscript numbers to

indicate number of e-'s in each sublevel.

Ex: C is 1s22s22p2 (cause 6 electrons)

Practice writing e- configurations

• Na

• O

• Ca

• C

• 1s22s22p63s1

• 1s22s22p4

• 1s22s22p63s23p64s2

• 1s22s22p2

The Periodic Table actually is arranged by s, p, d, and f sublevels.

5.11 S Orbitals

1s 3s2s

P Orbitals

Cool orbital pictureshttp://winter.group.shef.ac.uk/orbitron/

Ch. 5 Self Test p. 140

• Try # 1-4, 6-7, 9, 12, 14-15, 17-18

• Answers in Appendix J

• Try to answer first, then check your answer!

• Also work the problems in the online NOTES and worksheets.