Theories Change …

• The The Atomic Theory of MatterAtomic Theory of Matter states states that all matter is composed of small, that all matter is composed of small, fast moving particles called atoms. fast moving particles called atoms. These atoms can join together to form These atoms can join together to form molecules. molecules.

• This theory is really thousands of This theory is really thousands of individual theories that provide individual theories that provide evidence for the whole theory. evidence for the whole theory.

HISTORY OF THE ATOMHISTORY OF THE ATOM

460 BC Democritus develops the idea of atoms

He pounded up materials in his pestle

and mortar until he had reduced them

to smaller and smaller particles which

he called

ATOMAATOMA

(greek for indivisible)

HISTORY OF THE ATOMHISTORY OF THE ATOM

1808 John Dalton

Suggested that all matter was

made up of tiny spheres that were

able to bounce around with perfect

elasticity and called them

ATOMSATOMS

Dalton’s Atomic Theory (1808)1. Elements are composed of extremely small

particles called atoms. All atoms of a given element are identical. The atoms of one element are different from the atoms of all other elements.

2. Compounds are composed of atoms of more than one element.

3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.

2.1

8 X2Y16 X 8 Y+

2.1

HISTORY OF THE ATOMHISTORY OF THE ATOM

1898 Joseph John Thompson

Found that atoms could sometimes

eject a far smaller negative particle

which he called an

ELECTRONELECTRON

HISTORY OF THE ATOMHISTORY OF THE ATOM

Thompson develops the idea that an atom was made up of

electrons scattered unevenly within an elastic sphere

surrounded by a soup of positive charge to balance the

electron's charge

1904

like raisins in a muffin.

Raisins in a Muffin MODEL

2.2

HISTORY OF THE ATOMHISTORY OF THE ATOM

1910 Ernest Rutherford

He fired Helium nuclei at a piece of gold

foil which was only a few atoms thick.

He found that although most of them

passed through. About 1 in 10,000 hit

HISTORY OF THE ATOMHISTORY OF THE ATOM

gold foil

helium nuclei

They found that while most of the helium nuclei passed

through the foil, a small number were deflected and, to

their surprise, some helium nuclei bounced straight back.

helium nuclei

1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)

(1908 Nobel Prize in Chemistry)

2.2

atomic radius ~ 100 pm = 1 x 10-10 m

nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

Rutherford’s Rutherford’s Model of Model of the Atomthe Atom

2.2

HISTORY OF THE ATOMHISTORY OF THE ATOM

Rutherford’s new evidence allowed him to

propose a more detailed model with a central

nucleus.

He suggested that the positive charge was all

in a central nucleus. With this holding the

electrons in place by electrical attraction

However, this was not the end of the story.

HISTORY OF THE ATOMHISTORY OF THE ATOM

1913 Niels Bohr

Studied under Rutherford at the

Victoria University in

Manchester. Bohr refined Rutherford's idea

by adding that the electrons

were in orbits. Rather like

planets orbiting the sun. With

each orbit only able to contain a

set number of electrons.

Bohr’s Atom

electrons in orbits

nucleus

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

What do these particles consist of?

Name: Proton. Mass: 1 Charge: +1

Name: Neutron. Mass: 1 Charge: 0

Name: Electron. Mass: 1/2000 Charge: -1

All atoms are made up of just 3 basic sub-atomic particles:-

ATOMIC STRUCTUREATOMIC STRUCTURE

Notes: Atomic Theory

1. All atoms of a given element are identical. The atoms of one element are different from the atoms of all other elements.

2. Atoms are not created or destroyed in chemical reactions, they are only rearrange.

3. Compounds are composed of atoms of more than one element.

4. Subatomic particles are protons, neutrons and electrons.

5. Protons and neutrons are together in the nucleus

Notes: Atomic Theory

6. Electrons are in motion in orbits around the central nucleus.

7. Protons carry a positive electrical charge, electrons carry a negative charge, and neutrons carry no charge.

8. Neutrons work to keep nuclei together.

9. Most atoms are electrically neutral, meaning that they have an equal number of protons and electrons.

Notes: ATOMIC STRUCTURENotes: ATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

HeHe22

44 Atomic mass

Atomic number

Number of electrons = Number of protons

Symbol

Name

HeliumHelium

Isotopes are atoms with the same number of protons and different number of neutrons.

Isotopes are atoms of the same element (X) with different numbers of

neutrons in the nucleus

XAZ

H11 H (D)2

1 H (T)31

U23592 U238

92

Mass Number

Atomic NumberElement Symbol

2.3

2.3

How many protons, neutrons, and electrons are in C146 ?

How many protons, neutrons, and electrons are in C116 ?

6 protons, 8 (14 - 6) neutrons, 6 electrons

6 protons, 5 (11 - 6) neutrons, 6 electrons

Do You Understand Isotopes?

2.3

Let’s practice!!!

• Complete The Atoms Family - Atomic Math Challenge.

• Play with gizmo: www.explorelearning.com

Structure of the AtomStructure of the Atom• The Atomic Number of an atom = number of

protons in the nucleus.

• The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus.

• The number of Protons = Number of Electrons.

• Electrons orbit the nucleus in shells.

• Each shell can only carry a set number of electrons.

ATOMIC STRUCTUREATOMIC STRUCTURE

Electrons are arranged in Energy Levels

or Shells around the nucleus of an atom.

• first shell a maximum of 2 electrons

• second shell a maximum of 8

electrons

• third shell a maximum of 8

electrons

ATOMIC STRUCTUREATOMIC STRUCTURE

There are many ways to represent the atomic

structure of an element or compound.

One of them is:

1. Electronic Configuration

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

With electronic configuration elements are

represented numerically by the number of

electrons in their shells and number of shells. For

example;

N

Nitrogen

7

14

2 in 1st shell

5 in 2nd shell

configuration = 2 , 5

2 + 5 = 7

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

Write the electronic configuration for the following elements;

Ca O

Cl Si

Na20

40

11

23

8

17

16

35

14

28B

11

5

a) b) c)

d) e) f)

2,8,8,2 2,8,1

2,8,7 2,8,4 2,3

2,6

The Simplest AtomThe Simplest Atom

Name: Hydrogen

Atomic Symbol: H

Atomic Number (Number of Protons) = 1

Mass Number (Number of Protons + Neutrons) = 1

H 11

Atomic Number

Mass Number

The Next Simplest AtomThe Next Simplest Atom

He 42Name: Helium

Atomic Symbol: He

The centre of an atom is called the NUCLEUS

A Helium atom has two protons and two neutrons in its nucleus

The Next Simplest AtomThe Next Simplest Atom

Li 73Name: Lithium

Atomic Symbol: Li

Electron Configuration: 2,1

The orbit nearest the nucleus can only contain 2 electrons

so the third electron must be in a new orbit.

The Next Simplest AtomThe Next Simplest Atom

Be 94Name: Beryllium

Atomic Symbol: Be

Electron Configuration: 2,2

This orbit has room for 8 electrons

The Next Simplest AtomThe Next Simplest Atom

B 115Name: Boron

Atomic Symbol: B

Electron Configuration: 2,3

5p6n

Valence Electrons

• All the elements in a group have similar chemical properties as they have the same number of outer electrons which are called Valence electrons.

• For example: Group 1 Li and Na.

Period

Group

Alkali M

etal

Noble G

as

Halogen

Alkali E

arth Metal

2.4

Atoms and the Periodic Table.We can classify (arrange) elements in different ways:-

• naturally occurring/made by scientists

• solid/liquid/gas

• metal/non-metal

NOTES: The Periodic Table

1. The Russian scientist Dmitri Mendeleev published the first periodic table because he noticed a pattern of properties as he arrange elements by atomic mass.

2. Elements were rearranged by atomic number after the proton was discovered.

3. The properties of an element can be predicted from its location in the periodic table.

4. Each horizontal row of the table is called a period. 5. The elements in a column are called a group, or family. 6. The groups are numbered from Group 1 on the left to

Group 18 on the right.

Notes: The Periodic Table

7. Stars consist of matter in the form of plasma, a gas-like mixture .

8. Elements are created when the extreme high pressure inside stars forces atomic nuclei to collide.

9. This process is called nuclear fusion. 10. Nuclear fusion combines smaller nuclei into larger

nuclei creating heavier elements. 11. Electrons are arranged in Energy Levels around the

nucleus of an atom.12. They can hold 2 electrons in the first level, 8 in the

second and 8 in the third.13. The outer electrons are called Valence electrons, and

each Group has the same number.

MetalsThe physical properties of metals include:

• Shininess• Malleability: can be hammered or rolled into flat sheets and

other shapes. • Ductility: can be pulled out, or drawn, into a long wire. • Conductivity: ability to transfer heat or electricity.• Magnetic: Attracted to magnets and can be made into

magnets.• Solids: Most are, at room temperature.• Corrosion: Some metals react with oxygen in the air, forming

rust. • Reactive: Combines with other elements with ease and

speed. Metals usually react by losing electrons to other atoms. The reactivity of metals tends to decrease from left to right across the periodic table.

Notes: THE PERIODIC TABLEMETALS NONMETALS METALLOIDS

A substance or mixture that has a luster or shine, is generally a good conductor of heat & electricity, & is malleable & ductile. They can corrode and can become magnetic.

An element that does not exhibit the characteristics of a metal; they are generally solids or gases and are usually hard, brittle substances.

An element having both metallic and nonmetallic properties. They are usually good semiconductors

Except for mercury, the metallic elements are solids at room temperature (~20° C)

Bromine is the only liquid nonmetal.

Hydrogen

• Hydrogen belongs to a family of its own.

• Hydrogen is a diatomic, reactive gas.

• Hydrogen was involved in the explosion of the Hindenberg.

• Hydrogen is promising as an alternative fuel source for automobiles

Alkali Metals

• 1st column on the periodic table (Group 1) not including hydrogen.

• Very reactive metals, always combined with something else in nature (like in salt).

• Soft enough to cut with a butter knife

Alkaline Earth Metals

• Second column on the periodic table. (Group 2)

• Reactive metals that are always combined with nonmetals in nature.

• Several of these elements are important mineral nutrients (such as Mg and Ca

Transition Metals

• Elements in groups 3-12

• Less reactive harder metals

• Includes metals used in jewelry and construction.

• Metals used “as metal.”

Boron Family

• Elements in group 13• Aluminum metal was

once rare and expensive, not a “disposable metal.”

Carbon Family• Elements in group 14• Contains elements

important to life and computers.

• Carbon is the basis for an entire branch of chemistry.

• Silicon and Germanium are important semiconductors.

Nitrogen Family• Elements in group 15• Nitrogen makes up over

¾ of the atmosphere.• Nitrogen and

phosphorus are both important in living things.

• Most of the world’s nitrogen is not available to living things.

• The red stuff on the tip of matches is phosphorus.

Oxygen Family or Chalcogens

• Elements in group 16• Oxygen is necessary

for respiration.• Many things that

stink, contain sulfur (rotten eggs, garlic, skunks,etc.)

Halogens

• Elements in group 17• Very reactive, volatile,

diatomic, nonmetals• Always found

combined with other element in nature .

• Used as disinfectants and to strengthen teeth.

• Salt forming.

The Noble Gases

The Noble Gases

• Elements in group 18• VERY unreactive,

monatomic gases• Used in lighted “neon”

signs• Used in blimps to fix

the Hindenberg problem.

• Have a full valence shell.

Notes:The Periodic Table (12 parts)

Alkali Metals 1ve

Alkaline Earth Metals 2ve

Boron Family 3ve

Carbon Family 4ve

Nitrogen Family 5ve

Halogens Family 7ve

Oxygen Family 6ve

Noble Gases Family 8ve

Transition Metals

Lanthanides

Actinides Transition Metals, Lanthanides and Actinides have different number of valence electrons.

Hydrogen 1ve

Notes: The Periodic Table

14. Elements that follow uranium are made when nuclear particles are forced to crash into one another.

15. Elements with atomic numbers above 92 are synthetic and are made in nuclear reactors or powerful machines called particle accelerators .

16. Semiconductors are substances that under some conditions can carry electricity, and under other conditions cannot carry electricity.

Links

Webelements.comInteractive Periodic TableThe Visual Elements Periodic TableChemical ElementsLos Alamos National Laboratory Additional Physics Tutorials

Notes: Radioactivity1. In a process called radioactive decay, the atomic nuclei of

unstable isotopes release fast-moving particles and energy.

2. In 1896, the French scientist Henri Becquerel discovered radioactive decay quite by accident while studying a mineral containing uranium.

3. Becquerel presented his findings to Marie Curie and her husband Pierre .The Curies concluded that a reaction was taking place with the uranium nuclei.

4. Radioactivity is the name that Marie gave to this spontaneous emission of radiation by an unstable atomic nucleus.

5. Natural radioactive decay can produce alpha particles, beta particles, and gamma rays.

Notes: Radioactivity6. The particles and energy produced during radioactive decay are

forms of nuclear radiation.7. An alpha particle consists of two protons and two neutrons and

is positively charged. It is the same as a helium nucleus. Alpha radiation can cause an injury much like a bad burn.

8. After alpha radiation the atomic number is decreased by 2 and the atomic mass by 4.

9. A beta particle is a neutron that changes into a proton and a negative beta particle. Beta particles can travel into the body and cause cell damage.

10. After beta radiation the atomic number increases by 1 and the atomic mass decreases by 1.

11. Alpha and beta decay are almost always accompanied by gamma radiation which is detectable.

12. Gamma radiation is high-energy waves. Gamma rays can pass right through the human body, causing severe cell damage.

Notes: Radioactivity13. Uses of radioactive decay include tracing the steps of

chemical reactions and industrial processes, and diagnosing and treating disease.

14. Tracers are radioactive isotopes that can be followed through the steps of a chemical reaction or an industrial process.

15. In addition, the radiation given off by certain radioactive isotopes can be used to destroy unhealthy cells in the body, such as those in cancer tumors.

16. Nuclear Decay Gizmo

Notes: Half-life1. Half – life2. As a radioactive element within a rock or object

decays, it changes into another element.3. Therefore, the composition of the object

changes slowly over time. The amount of the radioactive element decreases. But the amount of the new element increases.

4. The half-life of a radioactive element is the time it takes for half of the radioactive atoms to decay.

Notes: Half-life5. Scientists often use potassium-40 to date

rocks. This form of potassium decays to form the stable element argon-40 and has a half-life of 1.3 billion years. The long half-life of potassium-40 makes it useful in dating the most ancient rocks.

6. Carbon-14 is useful in dating materials from plants and animals that lived as far back as 50,000 years ago. Because carbon-14 has a half-life of only 5,730 years, it can’t be used to date more ancient fossils or rocks.

Notes: Half-life• Percentage What percentage of a radioactive element

will be left after 3 half-lives? First, multiply ½ three times to determine what fraction of the element will remain.

• You can convert this fraction to a percentage by setting up a proportion:

• To find the value of d, begin by cross multiplying, as for

any proportion: • Practice Problems What percentage of a radioactive

element will remain after 5 half-lives?

Links to radioactivity• BrainPop Movie

• Nuclear Decay Gizmo

• Uses of Radiactivity