Chapter 14 Section 1061851f72b23d802adaa-d56582058559818728a814bdd94ad99a.r54.cf2.rackcdn…• Chapter 14 Section 1 What is matter? Matter is anything that has mass and takes up space

Chemistry

• Chapter 14 Section 1

What is matter?

Matter is anything that has mass and

takes up space

What is matter made of??

Atoms.

All matter is made of atoms.

Atoms are the building blocks of Matter

There is also an Atomic Theory

Different discoveries made by different

scientists led to today’s atomic model.

Contributors:

-Greeks

-Dalton

-Crookes

-JJ Thomson

-Rutherford

-Niels Bohr

-Schrodinger ( not in the book)

First Thoughts

• Greeks- believed matter is made of tiny

particles.

• Geeks named the tiny particles atom

• Atom = “uncuttable” in Greek

• now we know that the atom can be

divided into smaller particles by nuclear

reactions

**Science today and in the past

• Past – no means to perform a lot of

experiments

• Discoveries were based in discussions,

observations and reasoning

• There were philosophers instead of

actual scientists

**Science and Technology today

• Technology –allows us to perform

experiments and to develop and prove

theories

• That is why knowledge in constantly

evolving

• Technology gives us the tools to do

Science

Understanding the structure of the

atom

The model of the atom changed over

time

Electrons (-) charge

Protons (+) charge

Neutrons have no charge

• How is that the atomic model evolved

from Dalton’s model to today’s model?

Dalton’s Ideas – early 19th century

1. Matter is made up of atoms - correct

2. Atoms can’t be divided into smaller parts -

wrong

3. All the atoms of an element are exactly alike –

almost correct - isotopes

4. Different elements are made of different atoms

– correct – Element gold has only atoms of gold

5. His model: a hard sphere like a marble. ( fig. 3)

Crookes - brought some evidence of Dalton’s

ideas.

Late 19th century

• Using a cathode ray tube without air

• Demonstrated the presence of particles

in matter

Thomson experiment(1897)

used the CRT to understand what were those

particles

Thomson understood that:

The particles in the CRT have a (-) charge

These particles are in all materials

These particles were later called atoms

Thomson’s conclusions and Atomic Model

Atoms have (-) particles

But matter is neutral, it is not negative

*So the atom must have also + charges

Thomson created a new

Model of the atom with (+)

and (-) particles

The (+) particles are called

protons

Rutherford’s Experiments ( 1906)

• Scientists needed more evidence to support Thompson’s model

• Rutherford discovered the nucleus and described a new model of the atom

How did he discover the nucleus?

Rutherford’s Experiment – fired (+) particles at a

thin sheet of gold.

Real Results:

The deflected particles passed close to a + area: nucleus

The repelled ones hit a positive area: nucleus

The ones that passed ( majority) hit a – area: electrons

Rutherford’s Model

The Nucleus

Almost all of the mass of the atom and all of its positive charges are located in a small region at the center of the atom called the nucleus.

The (+) particles were later called PROTONS

So far scientists knew that the atoms has:

1) A nucleus in the center with positive

particles called protons

2) Tiny Negative particles called

electrons that move around the

nucleus

3) Almost all the mass of the atom is

concentrated in the center

• We still have to understand how the

NEUTRON was discovered.

How was the Neutron discovered?

1) Atoms have electrons and protons

2) Electrons have very little mass, so…..

3) The mass of an atom should have been approximately equal to the mass of its protons, but…..

4) The mass of most atoms is at least twice as much as the mass of its protons.

WHERE is the rest of the mass coming from?

• There must be something else in the

nucleus to account for the extra mass.

• This third particle, which was later

call the neutron would have the same

mass as a proton and be electrically

neutral.

• It was difficult to find the neutron

because the neutron has no charge

The model of the atom was revised :

The central nucleus with

protons and neutrons

The electrons surrounding

the nucleus moving in orbits.

Niels Bohr (1913)

Today we know that:

Electrons are in constant, unpredictable motion and can’t be described by moving in an orbit.

The model of the atom was revised again.

*Erwin Schrodinger Model or

Electron Cloud Model ( 1926) – current model

• Electrons travel in a region surrounding the nucleus, which is called the electron cloud.

• The electrons can be anywhere, most likely close to the nucleus, attracted by the + forces

You should know:

The model of the atom as we know today

The particles name, where they are in the

atom and its charges

******In a neutral atom the number of

protons and electrons are the same

The importance of Technology in the

development of Science