Chapter 4

The Greeks thought that matter was composed of fire, earth, water, and air.

400BC Greek philosophers Thought all matter

was made up of atoms, which are the basic, indivisible particles of matter (atomos)

Alchemists-tried to turn cheap metal into gold

Believed all matter was continuous-did not believe in atoms

His theory (explanation) was accepted for nearly 2000 years

Performed the first quantitative experiments.

He studied the relationship between pressure and volume and came up with the definition of an element.

The father of modern chemistry. He wrote the first chemistry book.

Performed quantitative experiments where he weighed the reactants and products and verified the law of conservation of mass.

Scientists agreed that1. Most natural materials are mixtures of

pure substances.2. Pure substances are elements or

compounds.3. Law of constant composition (Law

of definite proportion or Proust’s Law)-a compound always has the same composition.

English schoolteacher who tied all three laws together in his atomic theory

Dalton turned Democritus’s idea into a scientific theory that could be tested by experimentation.

1. Elements are made of tiny particles called atoms.

2. All atoms of a given element are identical.

Atoms of different elements are different.

3. Atoms of one element combine with others to form compounds.

4. Atoms are indivisible in chemical processes. A chemical reaction changes the way the atoms are grouped together.

He came up with the law of multiple proportions-when two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.

Water (H2O) has 8 g of oxygen per 1 g of hydrogen.

Hydrogen peroxide (H2O2) has 16 g of oxygen per 1 g of hydrogen.

16/8 = 2/1 Small whole number ratios.

Mercury has two oxides. One is 96.2 % mercury by mass, the other is 92.6 % mercury by mass.

Show that these compounds follow the law of multiple proportion.

Speculate on the formula of the two oxides.

Gay-Lussac- compounds always react in whole number ratios by volume if they are under constant temperature and pressure.

Avogadro- interpreted that to mean that at the same temperature and pressure, equal volumes of gas contain the same number of particles (Avogadro’s Hypothesis)

Cathode-ray experiment: showed that the atoms of any element can be made to emit tiny negative particles

Determined the charge ratio of electrons

Voltage source

+-

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive end.positive end.

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field, he found that By adding an electric field, he found that the moving pieces were negative the moving pieces were negative

+

-

Found the electron, but couldn’t find where the positive charge was located.

Plum pudding model-a bunch of positive stuff with the electrons able to be removed.

Oil

Atomizer

Oil droplets

Telescope

-

+

X-rays

X-rays give some electrons a charge.

From the mass of the drop and the charge on the plates, he calculated the mass of an electron.

Some drops would hover

Discovered by accident by Henri Bequerel

Three types ◦ alpha (α)- helium nucleus (+2 charge, large

mass)◦ beta (β)- high speed electron◦ gamma (γ)- high energy light

Gold foil experiment, which led to the discovery of the nucleus.

Used uranium to produce alpha particles.

Aimed alpha particles at gold foil by drilling a hole in a lead block.

Like bullets through a tissue

Lead block

Uranium

Gold Foil

Florescent Screen

What he expected

Because, he thought the mass was evenly distributed in the atom.

What he got

How he explained it

+

Atom is mostly empty Small dense,

positive pieceat center.

Alpha particlesare deflected by

it if they get close enough.

+

The atom is mostly empty space.

Two regions Nucleus- protons

and neutrons. Electron cloud-

region where you might find an electron.

The number of protons in an atom determines the element’s identity

Nuclear forces hold the nuclear particles together

The atomic number equals the number of protons

Very small If the nucleus is a grape, the electrons would be about one mile away.

Have a negative charge The arrangements of electrons

determines the element’s chemical properties.

Mass number= protons+neutrons Neutrons=mass number-atomic number Isotope-atoms that have the same

number of protons and electrons but different numbers of neutrons (disproves point 2 of Dalton’s theory)

Nuclide-any isotope of any element

Z - atomic number = number of protons (determines type of atom).

A - mass number = number of protons + neutrons.

Number of protons = number of electrons (if neutral).

XA

Z

Na23

11

Mercury Sodium Carbon 13C 6

Mercury 80p, 80e, 121n Sodium 11p, 11e, 12n Carbon 6p, 6e, 6n 13C 6p, 6e, 7n 6

An ion is formed when we remove or add an electron to a neutral atom.

Cation-a positive ionAnion-a negative ion

Regular sodium has 11 electrons, 11 protons, and 12 neutrons. If we take away 1 electron, it would have 10 electrons (-), and 11 protons (+) so the charge would be +1. (Neutrons would stay the same).

Periodic TablePeriodic Table

Groups/families-vertical columns

Periods-horizontal rows

ConductorsLose electrons (cations +)Malleable and ductile

BrittleGain electrons (anions -)Covalent bonds

Alkali Metals

Alkaline Earth Metals

Halogens

Transition metals

Noble Gases

Rare Earth Metals(Inner transition metals)

Group Charge1 +12 +213 +314 +-4

Group Charge15 -316 -217 -118 none

+1

+2

-1-2-3+2

+1

-4

+3

Notice that metals tend to give up electrons while nonmetals tend to gain electrons.

Contains a metal and a nonmetal (causes ions that is why it is called ionic)

The net charge of an ionic compound has to be zero.

Sodium chloride Na +1 Cl -1 NaCl

Magnesium chloride Mg +2 Cl -1 MgCl2