Quick Chapter 4The Atom!

In the Beginning…Democritus: Thought everything

had little particles.◦Termed these invisible particles as

“atoms”◦Atomos: “uncut” or “indivisible”

Aristotle: Didn’t think this way◦Gave us four “elements”◦Earth, Wind, Fire, Water

Oh Johnny BoyJohn Dalton: Teacher (Yay!)

◦Discovered existence of atoms by measuring the masses of elements that form when compounds are made.

Dalton proposed a theory that all matter is made up of atoms, which cannot be divided.

Dalton’s Theory of Atoms (Not all of these are still correct)1. All elements are composed of atoms.

2. All atoms of the same element has the same mass while other elements have different masses.

3. Compounds contain atoms of more than one element.

4. Atoms of different elements always combine in the same way.

Double J ThomsonShowed that there are particles

in an atom that have a negative charge.

Thomson also showed that atoms are made of smaller particles.

Protons and electrons were thought to be evenly scattered throughout the atom like plum pudding

Rutherford’s ExperimentErnest Rutherford showed that

there is a positively charged center of an atom.

Nucleus: Dense, positively charged mass in the center of the atom.

Rutherford’s ConclusionBy 1920, Rutherford showed the

existence of two subatomic particles and predicted a third subatomic particle.

These are protons, electrons, and neutrons.

The Three Subatomic ParticlesProtons: Positive particle located in the

nucleus◦Discovered by Rutherford

Electrons: Negatively charged particle found outside of the nucleus◦Discovered by J.J. Thomson

Neutrons: Neutral particle found in the nucleus◦Discovered by James Chadwick

3 Things that separate E,P, and N

Mass •P and N have same mass 1 Atomic mass unit (Amu)•2000 E = about 1amu

Charge •E= Negative•P= Positive•N= Neutral

Location •P and N found in nucleus•E found outside of nucleus

Nova Now 12 minutes- CERNhttp://www.pbs.org/wgbh/nova/sc

iencenow/3410/02.html

Cosmic perspectivehttp://www.pbs.org/wgbh/nova/sc

iencenow/dispatches/070711.html

Atomic Number and Mass NumberAtomic Number: The number of

protons in an element◦Identifies an element◦Atomic number of an element never

changes

Mass Number: Sum total of Neutrons and Protons in a nucleus

How to find number of NeutronsMass Number - Atomic Number =

Number of Neutrons

Example: If an element had an mass number of 12 and an atomic number of 6, how many neutrons does it have?

12-6 = 6What element has an atomic number

of 92 and a mass number of 238?How many neutrons does it have?

Correcting DaltonIsotopes: Have same atomic

number but different mass numbers because of different number of neutrons◦Usually are Radioactive too!

Identifying IsotopesOxygen with different # of

neutrons

◦Oxygen-16: has 8 neutrons (Standard)

◦Oxygen-17: has 9 neutrons

◦Oxygen-18: has 10 neutrons

Bohr’s ModelNiels Bohr: Electrons move in the

definite orbits around the nucleus

He studied with Rutherford but focused on electrons rather than the nucleus

I’ve got the power!Electrons in Bohr’s Model move at a constant

speed

Each electron of an atom has a specific amount of energy

Energy levels: Possible energies that electrons in an atom can have

Electrons can move from one energy level to another when the atom gains or loses energy.

Improved Bohr’s ModelHe was right about energy levels

but wrong about electron movement

Electron cloud: Visual model of the most likely locations for electrons in an atom

More of like a blur with hints at where electrons may be

OrbitalsOrbital: a region of space

around the nucleus where an electron is likely to be

Electrons near nucleus has low energy

Electrons away from nucleus has high energy

The chart of orbitals and energy levelsEach orbital can only hold 2

electrons

However each energy level can hold a certain amount of electrons

This is shown in the chart following: Know this chart

The ChartEnergy Level

Number of Orbitals

Maximum Number of Electrons

1 1 2

2 4 8

3 9 18

4 16 32

Configure your ElectronsElectron Configuration: arrangement

of electrons in the orbitals of an atom

Ground State: all electrons have the lowest possible energies

If an electron moves toward a level closer to the nucleus it loses energy

Away from the nucleus it gains energy

I’m so excited!When an atom absorbs enough

energy, an electron can move to an orbital with higher energy

Excited State: Electron moved to higher energy orbital and is less stable

Sub-Sub Atomic ParticlesQuark-found in the

nucleus

A newly hypothesized. subatomic particles

Makes up all other particles in the nucleus

Extremely small