Atomic Structure

Atoms have parts• Nucleus– Nucleus houses the protons and neutrons of the

atom.• Circling the nucleus are the electrons

Protons

• Have a positive charge of +1• Determines the atom’s identity• Has an atomic mass of 1.0073 amu

AMU

• AMU (atomic mass unit) is defined as 1/12 the mass of a carbon atom.

• This makes every proton and neutron approximately equal to 1 amu.

• Electrons have such a small atomic mass that they are not factored into the atomic mass of an element.

Atomic Number

• Periodic table is laid out in order of increasing atomic number.

• Atomic number = elements # of protons• Every element has a unique atomic number

Atomic Mass

• Atomic mass is determined by adding together protons and neutrons

• Isotope- Elements that have differing numbers of neutrons.

• Most well known isotope is carbon 14

Atomic Mass

• True atomic mass is determined as the average mass of an element’s naturally occurring atom

• Determined using the percent abundance of each isotope of that atom.

Electrons

• Number of electrons determines overall charge of the atom

• A neutral atom must have same number of electrons as the number of protons

• If number of protons and electrons are not equal the atom is called an ion

Symbols

• All known elements have a symbol on the periodic table

• We can write symbols like this to indicate more information about the element

The Atomic Theory• John Dalton in 1808 composed Dalton’s

atomic theoryThree parts1. Each element is composed of tiny

indestructible particles called atoms.2. All atoms of a given element have the same

mass and other properties that distinguish them from the atoms of other elements

3. Atoms combine in simple, whole-number ratios to form compounds- Law of Definite Proportions

J.J. Thompson

• Discovered the electron– They have a negative charge– Much smaller than atoms– Proposed that atoms must have positive charge to

balance the negative charge

Plum pudding model of the atom: In the model suggested by J. J. Thomson, negatively charged electrons (yellow) were held in a sphere of positive charge (red).

Ernest Rutherford

• Gold Foil Experiment

Nuclear Theory

• Rutherford’s findings caused him to develop the nuclear theory of the atom

1. Most of the atom’s mass and all of its positive charge are contained in a small core called the nucleus.

2. Most of the volume of the atom is empty space through which the tiny, negatively charged electrons are dispersed.

3. The number of negatively charged electrons outside the nucleus is equal to the number of positively charged particles (protons) inside the nucleus, so that the atom is electrically neutral.

The Periodic Table

• Metals• Nonmetals• Metalloids• Groups/families• Periods• Main group, transition, Rare-Earth Metals

Periodic Table cont.

• Alkali Metals• Alkaline Earth metals• Halogens• Noble Gases• Lanthanides• Actinides

Ions

• Predicting Ion charges• Positive ions – Cations• Negative ions – Anions• Other known ion charges– Zn, Cd, Ag