STUDYING ATOMS

Ch. 4.1

True False Statement True False

Daltons atomic theory said all matter is made of atoms, which can

be divided

Thomson’s atomic model, showed that atoms are even smaller than

thought

Rutherford’s atomic model showed that the positive charge is contained

in the nucleus

Thomson’s model is also called the plum pudding model

Rutherford was the 1st to propose an atomic theory

Greek Atom- 2500 years ago Democritus- Greek philosopher

Atom from atomos – uncut, indivisible Different types of atoms with different

properties

Aristotle's Model :

Dalton’s Atomic Theory- 1800’s

Evidence Measured masses of

compounds Found that the ratio

of masses of the elements in a compound is always the same

Fixed composition!

Theory All elements are composed

of atoms All atoms of the same

element have the same mass, and atoms of different elements have different masses

Compounds contain atoms of more than 1 element

In a particular compound, atoms of different elements always combine in the same way

Dalton Summed Up:

All matter is made of individual particles, called atoms, which cannot be divided!

Thomson’s Experiment

Glass tube without air 1 side positive, 1 side negative Glowing beam appears in middle

Thomson’s Model of the Atom-1870’s

Evidence Negative charge

attracted to positive charge

1st evidence atoms are made of even smaller particles

Model Atom = neutral Negative and

positive evenly mixed

Called Plum Pudding after English dessert

Rutherford’s Experiment

Aimed alpha particles at gold screen Screen flash when struck by alpha

particle Traced path of alpha particles

Rutherford’s Atomic Theory-1900’s

Evidence Alpha particles- fast

moving positive charge

Positive is not evenly spread

Nucleus- dense, positively charged mass at atoms center

Theory All of an atoms

positive charge is concentrated in the nucleus

THE STRUCTURE OF AN ATOM

Ch. 4.2

True False Statement True False

Isotopes have the same atomic #, but different masses due to protons

The atomic # equals the # of protons in the element

The mass # is the sum of the protons and electrons

Protons and neutrons have almost identical masses

Protons, neutrons and electrons are subatomic particles of the atom

Subatomic Particles

Protons- Rutherford Positively charged particle found in the nucleus Same as atomic #

Electrons- Thomson Negatively charged particle found outside the

nucleus Atomic # - charge

Neutrons- Chadwick Neutral particle found in nucleus Mass almost exact to the proton Mass # - Atomic #

Comparing Subatomic ParticlesParticle Symbol Charge Relative

MassActual Mass

Electron e- 1- 1/1836 9.11 x 10-28

Proton p+ 1+ 1 1.674 x 10-24

Neutron n 0 1 1.674 x 10-24

Proton and neutrons= same ________

Atomic Number

Atoms of any given element always have the same # of p+

Every p+ is balanced by e- for a neutral charge

= # of e- in an atom of that element

= the # of p+ in an atom of that element

Because atoms are neutral!

Mass Number

= p+ + n

Ex: Al 13 p+ 14 n Mass # = 27

n = mass # - atomic #

Ex: Al Mass # = 27 Atomic # = 13 n= 27-13 14

Practice

Symbol Atomic #

Mass # Protons Electrons

Neutrons

Na 23 12

K

P

O

W

Isotopes

Every element does have the same # of protons and electrons

Neutrons can vary

Have the same atomic #, but different mass # due to neutrons

Practice

Symbol Atomic #

Mass # Protons Electrons

Neutrons

Be

Be+2 4 9 4 2 5

Cl

Cl-1

Na+3

MODERN ATOMIC THEORY

Ch. 4.3

True False Statement True False

Bohr’s model focused on electrons, and was adapted from Thomson

Electrons can jump energy levels by gaining or losing energy

Electron clouds are the likely areas in which you can find electrons

The higher the energy the fewer the atomic orbitals; the lower the

energy the higher # of orbitals

Electron configuration is based on lettering the periodic table- s, p d,

and e

Bohr’s Model

Partnered with Rutherford

Focused on electrons

Count the # of electrons, and place in orbit

Energy Levels

Energies that electrons can have

Electrons move levels when the atom gains or loses energy

Use with Bohr Models

Practice

B

Mg

Si

Ne

Electron Cloud Model

Improved Bohr Model

Visual model for most likely locations for electrons

Dense= electrons

Atomic Orbital's

Electron cloud = good approximation of how electrons behave in orbitals

Energy Level # of Orbitals Max # of Electrons

1 1 2

2 2 8

3 9 18

4 16 32

Electron Configuration

Arrangement of electrons in the orbitals Most stable = electrons in orbitals with

lowest energy Ground State= all electrons have lowest

energies

C= 1s22s22p2 Cr= 1s22s22p63s23p64s23d4

Practice

Li

Mg

K

Lewis Dot Structures

Count valance electrons (outer layer of electrons)

Place around element, no more than 8

Examples and rules for compounds

Practice

P

Be

Ca

CO2

HCl

NaCl