Atomic Atomic StructureStructure

Unit 3Unit 3

Atomic Structure Atomic Structure • If a nucleus were the size of baseball, a

baseball would be the over 3000 miles high.

• Nucleus- positive center of atom– makes up 99.9% of the atom’s mass.

• Electron cloud- contains negatively charged e-.– takes up virtually the entire volume of the

atom.

Atomic ParticlesAtomic Particles

Charge mass (amu) Location

Proton

Electron

Neutron

+1

0

1

1/1836

1

Nucleus

Nucleus

e- cloud -1

Atomic Particles (Cont.)Atomic Particles (Cont.)• atomic number: # of protons. • Protons identify the element. If the

# of protons changes, the element changes.

• Since all atoms are neutral, the: # of e- = # of p+

Atomic Particles (Cont.)Atomic Particles (Cont.)

• Atomic Mass (mass number) = # protons + # neutrons.

Atomic Mass

- Atomic #

# of Neutrons

C126

Atomic Mass

Atomic #

electron

neutron

proton

Mass NumberMass Number

Mass number is the number of protons and neutrons in the nucleus of an isotope.

Mass # = p+ + n0

Nuclide p+ n0 e- Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

Courtesy of Mr. Allen, El Diamante HS, Sciencegeeks.com

Relative Atomic MassRelative Atomic Mass• Masses of atoms expressed in grams

are very small. • For this reason, we use relative

mass.– The standard used by scientists to

govern units of atomic mass is carbon-12 atom. It has been arbitrarily assigned a mass of exactly 12 atomic mass units (amu).

Relative Atomic Mass (Cont)Relative Atomic Mass (Cont)• The hydrogen-1 atom has an atomic

mass of about 1/12 that of carbon-12 atom, or about 1amu.

• An oxygen-16 atom has about 16/12(or 4/3) the mass of carbon-12 atom…and so on

IsotopesIsotopes• Isotopes are alternate forms of an

element. They have the same number of protons but different numbers of neutrons and thus, different masses.

C126 C14

6 H 11 H 2

1 H 31

Atom AtomIsotope Isotope

Isotope

Isotopes (Cont.)Isotopes (Cont.)• If the atomic mass

on the periodic table matches the mass of your example, it is an atom. If not, it is an Isotope.

• Many Isotopes are radioactive forms of an element.

IsotopesIsotopes

Let’s PracticeLet’s Practice

Mg2512

P3115

# protons =

# electrons =

# neutrons =

12

1213

What is it?

An Isotope!

# protons =

# electrons =

# neutrons =

15

1516

What is it?

An Atom!

U23592

# protons =

# electrons =

# neutrons =

92

92

143

What is it?

An Isotope!

IonsIons• When the number of electrons

changes, the ‘atom’ now has a charge and is called an Ion.

• A Cation has more protons than electrons and is a positively charged ion: Na+1, Ca+2

• An Anion has more electrons than protons and is a negatively charged ion: O-2, Cl-1

Ions are ImportantIons are Important

Heart cell rhythm depends on the opening and closing of a complex series of valves on the cell membrane, called ion channels. Some valves let certain ions ike potassium (K+) flow out, others let different ions like sodium (Na+) flow in. There are also pumps that actively move ions one direction or another.

Courtesy of Mr. Allen, El Diamante HS, Sciencegeeks.com

Let’s PracticeLet’s Practice

Ca+24020

# protons =

# electrons =

# neutrons =

20

1820

What is it?

A Cation!

# protons =

# electrons =

# neutrons =

35

3645

What is it?

An Anion!

# protons =

# electrons =

# neutrons =

13

10

14

What is it?

A Cation!

Br -18035

Al+32713

Ions (Cont.)Ions (Cont.)• A Polyatomic Ion is an ion made of

different elements bound together. They can be positive or negative but are mostly negative.

• Ex: NH4+1; NO2

-1; SO4-2; PO4

-3.

• Atoms acquire this charge by gaining or losing electrons from their outer-most level = valence electrons.

Ions (Cont.)Ions (Cont.)

• Why would an atom do this? Because… Atoms with a full valence shell are more stable.

• The first level holds up to 2 electrons and all others hold 8.

P

N

8

8

2

Perhaps one of you gentlemen would mind telling me just what is outside the window that you find so attractive!

Atoms & IonsAtoms & Ions

More Atomic TheoryMore Atomic Theory

• Protons, neutrons and electrons are known to be separated into even smaller particles.

• “Quark” is the term of all the other particles located in the nucleus of an atom. Some types of quarks combine to form a proton. Other types combine to form a neutron.

The Quark…The Quark…

Oops…wrong Quark!

About Quarks…About Quarks…Protons and neutrons are NOT fundamental particles.Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.

Quarks are held together by “gluons”

Courtesy of Mr. Allen, El Diamante HS, Sciencegeeks.com

Build an AtomBuild an Atom

• http://www.pbs.org/wgbh/aso/tryit/atom/#

• Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element

• The average atomic mass of an element depends on both the mass and the relative abundance of each of the element’s isotopes.

• The average atomic mass can be calculated by multiplying the atomic mass of each isotope by its relative abundance(expressed in decimal form) and adding the results.

• Three isotopes of argon occur in nature Ar-36, Ar-38, and Ar-40. Calculate the average atomic mass of argon to two decimal places, given the following relative atomic masses and abundances of each of the isotopes .

• Ar-36(35.97 amu;0.337%), • Ar-38(37.96 amu; .063%, and • Ar-40(39.96 amu;99.600%)

[(35.97amu x 0.337)+(37.96amu x .063)+(39.96amu x 99.600)]/100 =OR[(35.97amu x 0.00337)+(37.96amu x .00063)+(39.96amu x .99600)] = 39.94amu

3 Laws of Atomic Theory3 Laws of Atomic Theory• Law of Definite Composition ─ a

compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound

• Example: teaspoon and a cup of sugar both are composed of 42.1 % carbon, 51.4% Oxygen & 6.5% Hydrogen

Law of Definite CompositionLaw of Definite Composition

CO molecules are always composed of 1 carbon and 1 oxygen. CO2 molecules are always composed of 1 carbon and 2 oxygens

Law of Conservation of MassLaw of Conservation of Mass• When two or more elements react to

produce a compound, the total mass of the compound is the same as the sum of the masses of the individual elements.

• Matter and mass is neither created nor destroyed.

Law of Multiple ProportionsLaw of Multiple Proportions

• This applies to different compounds made from the same element; the mass ratio for one of the elements that combines with a fixed mass of the other element can be expressed in a small whole number ratio.

Law of Multiple ProportionsLaw of Multiple Proportions

RadioactivityRadioactivity• Atoms that “break down” are said to

be radioactive.• There are eight other naturally

radioactive elements: polonium, astatine, radon, francium, radium, actinium, thorium and protactinium.

• All other man-made elements heavier than uranium are radioactive as well.