The Atom

400BC ish

Indivisible, Solid Sphere

ModelDeveloped by Democritus. He

said all matter is composed of

indivisible tiny things made up

into small not being able to be

seen by the eye structures.

400BC

Democritus

Democritus found that atoms are not all the same, they are eternal, and always moving. He made a theory on this to explain why and how atoms were so small, and what they were about. He proposed a more advance atomic theory.

http://www.philosophyprofessor.com/images/philosophers/democritus.jpg

First person to name tiny particle of matter the

ATOM

His theory (not completely accurate):

•All elements are composed of indivisible atoms

•All atoms of a given element are identical

•Atoms of different elements are different,

meaning different mass-wise

•Compounds are formed by the combination of

atoms of different elements .

•Law of Definite Proportion or Composition or

Ratio.

1803

John Dalton

He proposed the atomic theory. He inferred proportions of elements in compounds. He found the atomic weight, and chemical symbols. He also had the most useful atomic theory of matter. To come up with this, he tested gases and used evaporation to find out what the gases had on that mixture all together.

http://redescolar.ilce.edu.mx/redescolar/efemerides/septiembre2001/interna/dalton.gif

Theory

a. Basic unit of matter is a tiny particle

called atom.

b. All elements are composed of indivisible

atoms

c. All atoms of a given element are

identical.

d. Compounds are formed by the

combination of atoms of different elements.

1897

J.J. Thomson

He found electrons and subatomic particles

when he was working with cathode ray

tubes. He was working with glass tubes and

electricity and messed up and discovered

electrons.

http://www.phy.cam.ac.uk/cavendish/history/electron/jj_c1890.jpg

1897

Plum Pudding Model

Discovered by J.J. Thomson. He said the

atom was a sphere of positive electricity,

with negative particles throughout. This

came around right after he discovered the

electron.

Atomic Model Timeline

http://www.projectsharetexas.org/resource/

atomic-theory-dalton-thomson-and-

rutherfordontrack-chemistry-module-2-

lesson-1

1911

Ernest Rutherford

He ionized gas using radiation, and found alpha and beta waves. He used his research and the magnetic properties of

iron to find radio waves. He also discovered the atomic

nucleus using others research and findings. To find this he did

the Rutherford experiment. Briefly, he used a thin foil made of

gold metal to find positive and negative charges in an atom.

http://www.newgenevacenter.org/portrait/rutherford.jpg

Rutherford bombarded

gold foil with alpha

particles

Most passed through but

some were deflected

This is because alpha

particles are (+) and they

hit the dense (+) nucleus

of the gold atom thus

leading to the discovery of

the nucleus

https://www.youtube.com/watch?v=kBgIM

RV895w

Rutherford’s Gold Foil

1913

The Bohr Model

http://en.wikipedia.org/wiki/Bohr_model

Niels Bohr discovered this atom. It

shows a positively charged

nucleus surrounded by electrons.

This was mostly to explain the

Rydberg formula. The Bohr model

is a hydrogen model. It helps with

the learning of the quantum

theory.

1913

Niels Bohr

Niels figured out the structure of the atom, and their radiations. He also started the basis of the quantum theory.

http://www.nrc-cnrc.gc.ca/education/elements/images/elements/Bohrium.jpg

Most revolutionary model

Dense positive nucleus, with

electrons orbiting in shells

First model showing electrons

revolving around the nucleus

Based on past models and

experiments

Sodium Atom

Sodium atom shells

Bohr’s Model of the atom

https://www.youtube.com/watch?v=CUk

3enr-m0w

Discovered by

Thompson (-)

1/1836 amu

No charge,

subatomic particle

Subatomic particle,

1 amu (+)

An orbital is the area

where an electron can

most likely be found

Number of

protons+neutrons=atomic mass

Number of

protons=atomic numberAtomic

mass-atomic number=# of neutrons

Wave- Mechanical ModelAlso called the charge cloud model, orbital

model, or quantum mechanical model.

Unlike the Bohr model does not show the

path of the electrons in definite, fixed

orbits it shows the most probable location

of an electron with distinct amount of

energy in areas called orbitals.

1. Orbital: Most probable region in which an

electron can be located.

Wave-Mechanical Model

Atoms of the same element

with different number of

neutrons (atomic mass),

same number of protons.

Example:

Argon Isotopes

Naturally Occurring

Isotopes

Mass Number Natural

Abundance Half-life

36 0.3336% STABLE

38 0.0629% STABLE

40 99.6035%STABLE

Isotopes

Isotope Atomic mass (ma/u) Natural abundance

(atom %)

Nuclear spin (I) Magnetic moment

(μ/μN)

32S 31.97207070 (25) 94.93 (31) 0 0

33S 32.97145843 (23) 0.76 (2)

3/2 0.643821

34S 33.96786665 (22) 4.29 (28) 0 0

36S 35.96708062 (27) 0.02 (1) 0 0

1803

Dalton

1897

Thomson

1909

Rutherford

1913

Bohr

NOW

Outer electrons are known as valence

electrons

Quantum numbers:

s,p,d,f- each represent a sublevel and

orbital.

Each letter has a coefficient to signify

which level it is in

s can hold 2 electron

p can hold 6 electrons

d can hold 10 electrons

f can hold 14 electrons

e.g, oxygen: 1s2 2s2 2p4

Each orbital can hold no more than 2

electrons

Orbital notation:

1s2 2s2 2p3

You are not allowed to fill up

the second set of arrows

until you have finished

putting an arrow in each box

Ground State: in any given atom,

the electrons are found in the

lowest available energy level.

Excited State: when the

electrons move from lower

energy level to higher

energy levels. Unstable

Electrons can

absorb specific

amount of energy

called quanta (sing.

Quantum)

When the electron falls back its releases a quantum of energy..

This energy appears as a photon of radiation of definite wavelength…

The light emitted by an element when its electrons return to a lower energy state can be viewed as a Bright –line emission spectrum.

Bright Line Spectrum

The light emitted by an element when its

electrons return to a lower energy state

(excited state to the ground state)

Can be viewed as a bright-line spectrum

When an electron jumps to a

shell at a higher level it is

know to be at an excited

state

When it returns to ground

state, it produces a light

spectrum

Each element produces a

different spectra

http://science.hq.nasa.gov/kids/imagers/em

s/waves3.html

BRIGHT – LINE SPECTRUM

https://www.youtube.com/watch?v=N8_S

iS8OlSU

Homogenous Heterogeneous

Elements and compounds

are pure substance

(composition is same

throughout the material)

Law of Definite proportion:

atoms in compound exist in a

fixed ratio

Mixtures are like compounds

but can be separated

physically