The AtomReview Class #1

Greeks◦ Matter is made up of tiny, discrete particles

Fire, Earth, Wind, Water Boyle

◦ Found gold and silver as being elemental Dalton’s Theory

◦ All elements are composed of indivisible atoms◦ All atoms of a given element are identical◦ Atoms of different elements are different, that is,

they have different masses◦ Compounds are formed by the combination of

atoms of different elements

Theories of the Atom

JJ. Thomson◦ Cathode ray tube to show smaller units make up atom◦ Light ray deflected in a magnetic field◦ Came up with idea of electrons

PLUM PUDDING MODEL Nucleus

◦ Rutherford Bombarded atom with alpha particle Alpha particle got deflected Concluded atoms have a dense core – NUCLEUS

Because particles repelled, nucleus must be positive too Also concluded atom is mostly empty space

Electrons are distributed in the empty space

Experimental Parts of Atom – pg .3

Bohr◦ Dense nucleus◦ Electrons found in orbits

Electrons have required energy to keep them in orbit Not too much or too little Called this the planetary model

Wave Mechanical Model – modern model◦ Energy and matter can act as waves and particles

Solar panels◦ Dense positive center◦ Electrons are in “regions of probability”

Modern Atomic Model

RB pg. 4, 1-12

Questions

Nucleus contains 2 types of particles◦ Neutrons and protons

This is where the mass comes from Subatomic particles

◦ Mass of a proton is found on 1st page of reference tables

◦ 1 amu = mass of a proton = mass of 1 proton◦ Mass of electron is negligible

Structure of the Atom

Sum of number of protons and neutrons equals the mass number◦ Found in the periodic table as atomic mass◦ Measured in amu (atomic mass units) NOT grams

If measured in grams would be atomic mass * mass of an atom

Subatomic particles

All type of element on periodic table have the same number of protons◦ Protons define the element

Neutrons can vary from atom to atom for 1 element◦ Same # protons but different number neutrons =

isotopes Examples:

◦ Carbon – 12 = 6 protons and 6 neutrons◦ Carbon – 13 = 6 protons and _ neutrons

Isotopes

Mass number for element must be integer◦ We can’t have part of a proton or neutron◦ Why are atomic masses of elements not integers?

Weighted atomic mass◦ The atomic mass is an average of all the different

isotopes.◦ If have of the carbon isotopes were carbon 12 and

half were carbon 13 Weighted atomic mass would be 12.5 Is this the weighted atomic mass for carbon? Which isotope is more abundant?

Atomic masses

Found in space around a nucleus of an atom Energy Levels

◦ Orbitals in an atom form series of energy levels S holds 2 electrons P holds 6 electrons D holds 10 electrons

This is where S, P, and D block names come from

Electrons can move between energy levels◦ You can walk up a set of stairs, takes a certain

amount of energy◦ Certain amount of energy is needed for e- to jump

between energy levels (it is quantized)

Location of electrons

Ground state – e- in lowest energy◦ Ground state is given in periodic table on ref. tables◦ If e- configuration doesn’t match ground state, it has to

be excited state Excited state

◦ Electrons possess more energy than they would if they were in ground state

Spectral lines◦ Visible light that is emitted when electrons fall back to

their ground state◦ Must first add energy to be excited – we can’t see this

Ground vs excited state

RB pg. 7, 13-36

Questions

Read 9 – 16 for Wed. morning