Unit 1: Atoms

Level 3 Achievement Scale Can state the key results of the experiments associated with Dalton,

Rutherford, Thomson, Chadwick, and Bohr and what this lead each to conclude.

Can explain that the electrons are not massless but that in comparison to nucleus are insignificant to mass of the atom.

Can explain the role of the 3 fundamental forces (strong nuclear, weak nuclear and electromagnetic) in the atom.

Can determine the number of each of the subatomic particle in an atom when specifically given the atomic number, atomic mass, mass number, atomic mass unit and/or charge.

Can state the energy levels in which electrons exist when given an atom or ion and its charge.

Can explain that energy must be absorbed to change an atom from the ground sate to the excited state and that this transfer (absorption or emission) happens when electrons transfer between energy levels.

Can draw atomic models of atoms, ions and isotopes when given specific information (atomic number and mass, charge).

Atoms broken down further• Nucleus – Center of atom: Dense

– Protons and Neutrons: similar in size and mass• Protons – positive charge• Neutrons – no electric charge

• Outside the Nucleus– Electrons – cloud of tiny particles with little mass

• Electrons – negative charge (-1)

• Size – If the atom was the size of Brown’s stadium the nucleus would be the size of a small marble on the 50 yard line.

The Nucleus and Structure of the Atom

• Atoms are made of three kinds of particles: electrons, protons, and neutrons.

The mass of the electron is REAL small compared to protons and neutrons.

Number VS Mass

• Atomic Number– # of protons in an atom

• Atomic Mass– # of protons and

neutrons

Element = # protonsAtomic number

= # protons

Every Element had a certain atomic #

Isotope = relates to # neutrons

• All 3 are lithium because all 3 have same # of protons.

• Isotope: vary in mass because the # of neutrons differ.

ISOTOPES• Result when neutrons are added to an atom

• Vary in mass but are the same element because proton # is not changed

H1

H1

H12 3

C12

6

Mass Number(# protons + # neutrons)

Atomic Number(# protons)

Nuclear Notation

Mass # --- Atomic # = neutron #

12 – 6 = 6 neutrons

Neutral Atoms

• Uncharged atom–Results because

+ protons = - electrons

If you change the _____ ….

• If you change the PROTON, you change the _________

• If you change the NEUTRON, you change the _________

• If you change the ELECTRON, you change the _________

ELEMENT

ISOTOPE

ION

C14

6

How many protons?

How many electrons?

How many neutrons?

Draw a atomic model for this element?

6

6

82 4

Li 7

3

How many protons?

How many electrons?

How many neutrons?

Draw a atomic model for this element?

3

3

42 1

N 14

How many protons?

How many electrons?

How many neutrons?

Draw a atomic model for this element?

2 5

7

7

7

Ions

• Ion: An atom that has a charge

• Results from a loss or gain of an electron

• 1+ = loss of an electron

• 1- = gain of an electron

Mg25

12

2+

Protons =

Neutron =

Electrons =

12

13

10

Atomic Mass Unit

• AMU– Is equal to 1/12th of the mass of a carbon

atom– 1 AMU = isotope of carbon ( 6 protons / 6

neutrons)

• Average atomic mass – weighted avg.

The structure of the atom• Electrons are bound to

the nucleus by electromagnetic forces.

• The force is the attraction between protons (positive) and electrons (negative).

The momentum of the electron causes it to move around the nucleus rather than falling straight in.

The structure of the atom

• The strong nuclear force attracts neutrons and protons to each other, otherwise the positively charged protons would repel each other.

The structure of the atom• The weak force is weaker than both the electric force and

the strong nuclear force. • If you leave a solitary neutron outside the nucleus, the

weak force eventually causes it to break up into a proton and an electron.

• The force of gravity inside the atom is much weaker even than the weak force.

Every process we know in the universe can be explained in terms of these fundamental forces.

Forces• Electromagnetic

• Force that keeps the electrons from crashing into the nucleus – created by momentum

• Strong Nuclear• Force that keeps

the nucleus together – protons repel each other.

• Strongest force known to science

How do atoms function? Atoms are Picky! When a photon withexactly the right energycomes along, an electronwill be kicked into ahigher orbit

The photon is absorbed,and the electron jumps to higher (excited) state.

Electronic Energy States

• Electrons can only have certain energies; other energies are not allowed.

• Each type of atom has a unique set of energies.

Bohr model of the atom• Danish physicist Neils Bohr

proposed the concept of energy levels to explain the spectrum of hydrogen.

• When an electron moves from a higher energy level to a lower one, the atom gives up the energy difference between the two levels.

• The energy comes out as different colors of light.

Electrons in the atom

• Each different element has its own characteristic pattern of colors called a spectrum.

• The colors of clothes, paint, and everything else around you come from this property of elements to emit or absorb light of only certain colors.

Electrons in atoms• Each individual color in a spectrum is called a

spectral line because each color appears as a line in a spectroscope.

• A spectroscope is a device that spreads light into its different colors.

Electrons and energy levels• In the current model of the atom, we think of the

electrons as moving around the nucleus in an area called an electron cloud.

• The energy levels occur because electrons in the cloud are at different average distances from the nucleus.

Rules for energy levels

Inside an atom, electrons always obey these rules:

1. The energy of an electron must match one of the energy levels in the atom.

2. Each energy level can hold only a certain number of electrons, and no more.

2 8 8 18

3. As electrons are added to an atom, they settle into the lowest unfilled energy level.

Energy levels• In the Bohr model of

the atom, the first energy level can accept up to two electrons.

• The second and third energy levels hold up to eight electrons each.

• The fourth and fifth energy levels hold 18 electrons.

Fireworks• Heat added puts electrons at a higher energy level – coming down emits light.

• Different elements burn different colors because light is emitted a different wave frequencies

14.2 The quantum theory• Quantum theory says that when things

get very small, like the size of an atom, matter and energy do not obey Newton’s laws or other laws of classical physics.

14.2 The quantum theory• According to quantum

theory, particles the size of electrons are fundamentally different

• An electron appears in a wave-like “cloud and has no definite position.

14.2 The quantum theory• The work of German physicist Werner

Heisenberg (1901–1976) led to Heisenberg’s uncertainty principle.

• The uncertainty principle explains why a particle’s position, momentum or energy can never be precisely determined.

• The uncertainty principle exists because measuring any variable disturbs the others in an unpredictable way.

14.2 The uncertainty principle