Chapter 3 – Atoms: The Building Blocks of Matter

Section 3-1 – The Atom: From Philosophical Idea to Scientific

Theory

The first people to think about particle theory were the _____________ around

___________.

Greeks

400 BC

One in particular was __________. The word atom in

Greek means _______.

Democritus

indivisible

Following Democritus was _________. He didn’t believe in atoms. He thought matter was

___________.

Aristotle

continuous

This idea succeeded for about _______years. Neither view

was supported by __________ _________ until ________.

2000experimental evidence

The 18th century

By the late ________, most people thought of an _______ as

something that could not be broken down and that could _________

with other elements to form __________.

1800’s Atom

combine compounds

Scientists still weren’t sure, however if they always combined in the same

________.

proportions

In the late 1790’s scientists had better _________ which allowed

them to study chemical reactions ___________.

balances

quantitatively

This led to the law of _______________________. It essentially says that as long as

nothing enters or leaves a chemical reaction, _______ remains

constant.

conservation of mass

mass

Antoine-Laurent de Lavoisier

• He was obsessed with measuring mass during chemical reactions.

• He observed that when chemical reactions are carried out in a closed system, the mass of the system is not changed.

• He was obsessed with the latest equipment for measuring mass.

• He spent a great deal of the French taxpayers money on this equipment.

• He died in the French Revolution.

It also lead to the law of __________________ which

essentially says that regardless of the _________ or _________ of

the sample, the elements that make it up are always there in the same

____________.definite composition

size or sourceproportions

Law of Definite Proportions

Joseph Louis Proust observed that Copper carbonate (CuCO3) occurs in nature

as the mineral malachite (a), it forms as a patina on copper roofs (b) and bronze

statues, and can also be synthesized in the laboratory (c). Regardless of its

source, basic copper carbonate has the same composition.

Joseph Louis Proust (1754-1826)

Since the composition of copper carbonate is the identical regardless

of the source, Proust called this generalization as the law of definite

proportions.

Swedish chemist Berzelius

heated certain amount of lead

with various amount of sulfur. He

found that when he used 1.55 g of

sulfur (yellow) and 10.0 g of lead

(gray) he got 11.55 of lead sulfide

(black).Jons Jacob von Berzelius

1779-1848

If sulfur were taken in excess of 1.55g, Berzelius found that the excess

amount of sulfur did not react. Similarly if had 1.55 g of sulfur and added

lead in excess of 10.0 g, he found that the excess lead did not react

The law of definite proportions – Berzelius View

Definite proportions – A Closer Look

The law of definite proportions. Berzelius' experiment with lead and sulfur

are interpreted in terms of Dalton's atomic theory.

The electrolysis of water

Electrolysis of water. During electrolysis,

water decomposes to give hydrogen gas

and oxygen gas always in a 2-to-1 volume

ratio when energy is supplied by a battery

or other source of direct current (dc).

http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_04/Electrolysis_of_Water.MOV

Henry Cavendish (1731 - 1810) further

illustrated the law of definite proportion

by electrolyzing water.

More complicated is the law of ______________. It says that if ______ or

more different _______ are made of the same 2 elements, the ratio of the ________ element combined with a fixed mass of the 1st element is always a ________ of small

___________ numbers

multiple proportions two2nd ratio

whole

An example of this would be the compounds of ___________

and ___________.

carbon dioxide

carbon monoxide

John Dalton’s Atomic Theory of Multiple Proportions

John Dalton John Dalton (1766-1848)(1766-1848)

Dalton theory multiple proportions:

Elements can combine with each other

in more than one set of proportions.

For example, hydrogen and oxygen

combine with each other in two different

proportions and form two entirely

different compounds.

Water

OH2OH2 222 peroxideHydrogen

OH2O2H2 2222

Although these two

molecules contain only

hydrogen and oxygen,

they are not the same

compound.

These three laws prompted John Dalton to propose his

atomic theory. It basically says:

1. All matter is made of ______________

______________ called ____________

indivisibleindestructible

atoms

2. Atoms of the same ___________ are chemically and physically the ________.

element

same

3. Atoms of ___________ elements are chemically and

physically the ________.

different

different

4. When atoms _______ in a chemical reaction, they do so in ___________, ____________

number ratios.

combinesmall whole

In a chemical reaction, atoms aren’t ____________ or

____________, they are simply _____________.

createddestroyedrearranged

Section 3-2 – The Structure of the Atom

Atoms consist of ___________________ regions.

One of them contains the ___________________ and

___________________. It is called the ___________________.

2protons neutrons

nucleus

The other area surrounds the nucleus. It contains

___________________ particles called

___________________.

negatively charged

electrons

Actually ___________________,

___________________, and ___________________ are all

___________________.

protons neutrons

electrons subatomic particles

The electron was discovered by working with a tube that

contained a ___________________ at very

low pressure.

gas

When ___________________ passed through it, it would light

up. It is called a _________________________

____________.

an electrical current

cathode ray tube

The fact that the ray was deflected by a negative charged

showed that the ray had a ___________________ charge.

negative

The fact that the ray could move a paddle wheel demonstrated the ___________________

nature of the ray.

particle

The ray was actually made of ___________________.

electrons

The scientist credited with naming the

___________________ was ___________________.

electron

JJ Thomson

It stands to reason that where there is a negative charge, there

must be a ___________________ charge

to balance it.

positive

_________________________ and associates tried to bombard

___________________ with ___________________.

Ernest Rutherfordgold

alpha particles

They expected that most of the α particles would

________________________.

go straight thru (92%)

For the most part, this was true, but some were ___________________ and a very small percentage were

actually _____________________.

deflected (6%)

shot straight back (2%)

It took 2 years, but Rutherford developed a 2 part explanation. It

was:

• Atoms are mostly empty space

• Atoms must have a densely packed positively charged nucleus.

To summarize the ___________________,

___________________ are the lightest and can be found

______________________. They have a ________________ charge.

subatomic particles electronsorbiting the nucleus

negative

___________________ and ___________________ are the heaviest and are found in the

___________________.

Protonsneutronsnucleus

___________________ have a positive charge and

___________________ have ___________________ charge.

Protonsneutrons

no

Section 3-3 – Counting Atoms

neutral, atomic number, chlorine, proton, 17, electron

A neutral atom of chlorine would have 17 protons and 17 electrons if it is neutral.

Because chlorine has an atomic number of 17, it would have 17 protons and assuming it is neutral, it would have 17 electrons.

isotope, tritium, deuterium, protium, atomic mass, 1, 2, 3, hydrogen

The three isotopes of hydrogen are protium with an atomic mass of 1, deuterium with an atomic mass of 2, and tritium with an atomic mass of 3.

Hydrogen has 3 different isotopes. They are protium, deuterium, and tritium with atomic masses of 1, 2, and 3 respectively.

nuclide, superscript, subscript, hyphen notation, uranium, nuclear

symbol

You can indicate nuclides 2 different ways; Hyphen notation means you write the symbol with a dash and the atomic mass or you could use the nuclear symbol method where you write the symbol and put the atomic mass as a subscript to the upper left and the atomic number as a subscript to the lower left.

Example

• U-238

U23892

carbon-12, atomic mass unit

An atomic mass unit is defined as one twelfth of a carbon-12 atom.

average atomic mass, isotopes, percentage, naturally occurring

The average atomic mass of an element takes into account the percentages of the naturally occurring isotopes.

Average atomic mass can be calculated by multiplying the atomic masses of the isotopes by their naturally occurring percentage in a mixture.

mole, carbon-12, Avogadro’s number, molar mass

A mole is defined as 12 g of the carbon-12 isotope. It has Avogadro’s number of atoms. The molar mass of all other elements is compared to a mole of carbon-12.

Subatomic Particles

The atoms of all elements consists of positively charged protons,

neutral neutrons and negatively charged electrons. The protons

and the neutrons together are called as nucleons and they are

located at the nucleus of the atoms.

The number of protons in the nucleus of an atom determines the

atomic number (Z) and indicates the element's identity. For a

neutral atom, the atomic number also describes the number of

electrons around the nucleus.

The Atomic Number

Atomic Mass and Atomic Number

Mass number A (sum of protons and neutrons)

Atomic number Z (number of protons)

= number of neutrons.

While the number of protons in the nucleus defines an element's

identity, variations on the number of neutrons in the nucleus give

rise to different isotopes of the same element.

Isotopes of hydrogen

Mass Numbers and Atomic Numbers

The atomic number is equal to the number of protons in an atom

of that element. The mass number is the sum of the number of

protons and neutrons.