Atomic Theory and Structure

Atomic Theory

Atoms are the building blocks of matter.

Law of Definite Proportions

A chemical compound always contains the same elements in the same proportions by mass.

Law of Conservation of Mass

Matter cannot be created or destroyed in ordinary chemical and physical changes.

Law of Multiple Proportions

When 2 elements combine to form 2 or more compounds, the mass of 1 element that combines with a given mass of the other is in the ratio of small whole numbers.

Dalton's Atomic Theory

1. Matter composed of indivisible particles called atoms.
2. Each element's atoms are alike.
3. Atoms of different elements have different masses.
4. Atoms of different elements combine in whole numbers to form compounds.
5. In chemical reactions, atoms are rearranged, not created nor destroyed.

Which principles of Dalton's Atomic Theory are no longer true?

1. Matter composed of indivisible particles called atoms.
2. Each element's atoms are alike.

JJ Thomson

Experimented with cathode ray tube; Discovered electrons

Ernest Rutherford

Experimented with gold foil; Discovered atom is mostly empty space and the nucleus contains most of the atom's mass

Atom

The smallest piece of matter than can exist while retaining properties of that matter.

How many types of atoms does an element have?

An element only has 1 kind of atom.

Element

An element has only 1 kind of atom and unique properties.

What charge do atoms have?

Atoms have an electrically neutral charge.

Where is most of the atom's mass contained?

Nucleus

Where are protons and neutrons located?

In the nucleus

Where are electrons located?

In the electron cloud (also referred to as electron shell)

What charge does a proton have?

+1

What charge does a neutron have?

-1

What charge does a neutron have?

No charge

Which 2 subatomic particles have significant masses?

Protons & Neutrons

Coulomb's Law

Like charges repel and unlike charges attract. The closer the charges are, the stronger the force of attraction.

Strong Force

Holds the protons and neutrons together in the nucleus of an atom. The closely packs neutrons and protons creates the strong force which is stronger than the repulsive force.

Atomic Number

The total number of protons in the atom.

What unit is atomic mass measured in?

amu (atomic mass units); 1 amu is 1/12th the mass of one carbon atom

How do you find the atomic mass?

Add the number of protons and neutrons.

Isotope

Atoms of the same element with different number of neutrons.

What is the mass on the periodic table an average of?

Average of all the isotopes of the elements.

For an atom to be neutral, which two subatomic particles need to be balanced.

Protons and Electrons

Which subatomic particle controls an element's identity?

Protons

Anion

Negatively charged atom with more electrons than protons

Cations

Positively charged particles that have lost electrons.

How can you calculate the charge of an atom?

Protons - Electrons = Charge

Equation for Mass Number

Mass Number = protons + neutrons

What do neutrons affect?

Neutrons affect an atom's mass number.

What do protons affect?

Responsible for an atom's identity, affects mass number, and can affect atom's charge.

What do electrons affect?

Electrons affect an atom's charge.

Which part of the atom has the most mass?

Nucleus

What type of average is "average atomic mass"?

A relative average; it's the average of the isotopes compared to carbon.

Equation for Average Atomic Mass

Average Atomic Mass = (mass of isotope 1 x abundance) + ( mass of isotope 2 x abundance)

What unit can replace amu?

Grams

Alpha Particle

A small, positively charge particle, which Rutherford directed at thin, gold foil

Anode

The electrode attached to the positive terminal of a voltage source

Cathode

The electrode attached to the negative terminal of a voltage source