Chemistry:Matter and Chemical Bonding

Early Atomic Theories

Timeline. . . . .

Ancient Greeks (approx 450 BC) "Four Element" Theory – Earth, Air, Fire,

Water

Benefits:

First suggestion that substances were actually made up of a combination of different "elements."

Democritus:

400 BC – Democritus "The smallest indivisible particle of

matter is the 'atom' " No evidence – based on thought However, the "4 element" theory

lingered for almost 2000 years! (YIKES)

Democritus’ Model

John Dalton (1809) All matter is composed of indivisible

particles called atoms. All atoms of a given element are identical;

atoms of different elements have different properties.

Chemical reactions involve the combination of atoms, not the destruction of atoms.

When elements react to form compounds, they react in whole-number ratios.

Dalton's atomic theory supported previous research. Lasted almost a century!

Model: Indivisible billiard ball

J.J. Thomson (1897)

Used the work of other scientists that showed that atoms contain charges, and his own work with cathode ray tubes, to develop a modified atomic theory.

Atoms are positive spheres, with negative particles (electrons) embedded in them.

Model: Raisin bun

Ernest Rutherford (1911) Student of Thomson – disagreed.Gold Foil Experiment: Alpha radiation (positive) were shot at a

piece of gold foil. Most of the alpha particles passed through

the foil, suggesting that most of matter is empty space!

Some particles were deflected back at angles; they had come in contact with something very dense!

Gold Foil Experiment:

Leading to…..Nuclear Model: Rutherford – dense core of positive

charge (nucleus), with negative electrons orbiting around the nucleus.

Later experiments showed that the positively charged particles, now called protons, have an equal but opposite charge to the electrons, and have a mass 1836 x greater!

The neutron and the existence of isotopes were also discovered

Niels Bohr

Worked with Rutherford Used atomic spectrum information to

place electrons in energy levels around the nucleus

Spectroscope:

How it works…. Each element has a unique emission

spectrum When electrons are given energy,

they jump to a new energy level When they fall back down, they emit

this extra energy as light Lines on an emission spectrum

represent jumps between energy levels.

DEMO

Emission Spectra:

Modern View of the Atom

Dense nucleus containing: (+) protons Neutral neutrons

Shells of small (-) electrons orbiting the nucleus

2 e- in 1st orbital

8 in 2nd

8 in 3rd

(until next year)

Subatomic Particle

Charge Location Size

Proton (p+) Positive Nucleus 1

Neutron (n0) Neutral Nucleus 1

Electron (e-) Negative In Orbit 1_ 2000

Atomic mass / Mass Number-Use rounded values

-26.98 -> 27-28.09 -> 28-30.97 -> 31

Atomic Number= # of protons= # of electrons in a neutral atom

Mass number = protons + neutrons

Isotopes

Atoms of the same element have the same # of protons

The # of neutrons can differ The same element with a different # of

neutrons are called isotopes Radioisotopes are unstable and decay

creating radioactivity Average atomic mass takes the masses of all

isotopes into account.

Standard Atomic Notation

C

mass # is 12 atomic # is 6 therefore, this carbon has 12 - 6 = 6

neutrons

6

12

GROUPS ON THE PERIODIC TABLE

Your Turn

Subatomic Particle Worksheet Read 6.4

Define: Chemical Family, Periods, Dmitri Mendeleev

“Try this” on page 224 Homework

P. 225 Q: 1-6, 8-11