INSIDE THE ATOMINSIDE THE ATOM

Three Topics: Section 1

• How scientists model the atom

• What are charged particles

• What were Rutherford’s experiments

REVIEW VOCABULARY

Matter: anything that has mass and takes up space.

anode

electron cloud

cathode

neutron

alpha particle

proton

electron

element

New Vocabulary

electrode with a positive charge

region surrounding the nucleus in which electrons travel

electrode with a negative charge

particle in the nucleus of an atom that has the same mass as a proton and is electrically neutral

fast-moving, positively charge bit of matter

positively charged particle present in the nucleus of all atoms

negatively charged particle located outside the nucleus of an atom

matter made up of only one type of atom

Summarize early ideas about the structure of matter

Matter was made of tiny particles and could be cut into smaller and smaller pieces until reaching a piece that could not be cut any more.

This smallest piece is an atom.

FIRST THOUGHTS

Dalton’s Ideas Dalton’s Ideas About matterAbout matter

Matter is Matter is made up of made up of

atomsatoms

All atoms of All atoms of an element an element are exactly are exactly

alikealike

Atoms cannot Atoms cannot be divided be divided

into smaller into smaller piecespieces

Different Different elements are elements are

made of made of different kinds different kinds

of atomsof atoms

Anode +

Cathode -Mask

Shadow

Crooke’s Tube

Crooke’s Experiments

He connected a battery to cathode (-) and anode (+) of a tube. He found that an object in the middle of the tube (mask) cast a shadow in a green glow. He concluded that the glow was caused by rays, or streams of particles.

MAGNET

Rays are bent by magnet

CATHODE RAYS

thomson’s experiments

Thomson’s ExperimentsHe placed a magnet next to the tube. The ray was bent by the magnet, showing the ray was made of particles, not light. He envisioned an atom as a sphere of positive charge with negatively charged electrons spread out evenly within. This is sometimes called The Plum Pudding Model.

rutherford’s experiment

Rutherford’s ExperimentExperiment: Rutherford fired alpha particles at a thin film of gold. A screen lit up when it was hit by a charged particle.

Expected Result: Almost all the alpha particles would go straight through.

Actual Result: More particles bounced off than expected - some of them straight back!

Conclusion: Positive and negative charges not evenly spread out. Positive charge concentrated into a nucleus.

After Rutherford’s model, how the extra mass in the

nucleus was explained

How electrons are thought to move in the most current

atomic model

Describe the following improvements to atomic theory.

Neutron - neutral charge Electron Cloud

The Atom

Electrons

Nucleus

Protons

Neutrons

ElectronCloud

++

++

++

The Atom

particle location chargemass

(relative)

proton nucleus + 2000

neutron nucleus none 2000

electronelectron

cloud-- 1

Section 2: The Nucleus

• What is radioactive decay?

• What is half-life?

• How are radioactive isotopes used?

REVIEW VOCABULARY

Atom: Matter is made up of atoms.

New Vocabulary

number of protons in nucleus

atom of an element with different number of neutrons

number of neutrons plus number of protons

release of nuclear particles and energy

changing of one element into another through radioactive decay

high-energy electron that comes from the nucleus

amount of time it takes for half a sample of an element to decay

atomic number

isotope

mass number

radioactive decay

transmutation

beta particle

half-life

Section 2: The Nucleus

Carbon-12 Carbon-13 Carbon-14

Atomic number

Number of protons

Number of neutrons

Mass Number

6 6 6

6 6 6

6 7 8

12 13 14

Summarize what the strong nuclear force does.

It holds the protons and neutrons in the nucleus.

carboncarbon

66

CC1212

READING THE PERIODIC TABLE

Atomic Number = # of protons, # of electrons

Symbol

Atomic Mass = # protons + # neutrons

Name

Sequence steps of radioactive decay

NeutronNeutronbecomesbecomesunstableunstable

The electronThe electron

The protonThe proton

Neutron splitsinto electronand proton.

isejected with a largeamount of energy.

stays in the nucleus.

Atomic number increases by one.

HALF-LIFE

You have 100 grams of Iodine-131, which has a half-life of 8 days. How much will be left after 24 days?

100 100 gg

Begin

50 50 gg

8 days

25 g25 g

16 days

12.5 g12.5 g

24 days

1 2 3

HALF-LIFE

You have 16 grams of Element-X, which has a half-life of 10 days. How much will be left after 40 days?

16 g16 g

Begin

8 g8 g

10 days

4 g4 g

20 days

2 g2 g

30 days

1 g1 g

40 days

1 2 3 4

HALF-LIFE

You have 20 grams of Element-X, which has a half-life of 2 days. How much will be left after 6 days?

20g20g 10g10g

2 days

5 g5 g

4 days

2.5g2.5g

6 days

1 2 3

Rate of Decay

Start1st

HalfLife2nd

HalfLife3rd

HalfLife

Time Elapsed

Mass

0 days 8 days

20 g 10 g

16 days24 days

5 g 2.5 g

half-life the amount of time it takes for one half of a substance to decay.

Identify uses and hazards of radioactive material.

USESUSES HAZARDSHAZARDS

RadioactiveRadioactiveMaterialMaterial

Smoke detectorsMedicineDate fossilsEnergy

Radiation poisoning

Long half-life