•Chapter 4

Atomic StructureNote-taking Guide

•4.1 Defining the Atom• An atom is the smallest particle of an element that retains its identity in a chemical reaction.

• It is difficult to directly observe an atom because it is so small.

•Democritus Atomic Philosophy• He believed atoms were indivisible and indestructible.

• He was the first to suggest the existence of atoms but he lacked experiments to prove it.

•Dalton’s Atomic Theory• By using experimental connections, Dalton transformed previous ideas about atoms into a scientific theory.

•Dalton’s Atomic Theory• 1. All elements are composed of tiny indivisible particles called atoms.

• 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

• 3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.

• 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

•Sizing up the Atom

• Individual atoms are difficult to see because they are so small.

• Despite their small size, atoms are observable with instruments such as scanning tunneling microscopes.

•4.2 Structure of the Nuclear Atom• There are three kinds of subatomic particles in an atom.

• Proton, neutron and electron.• Protons are positive.• Electrons are negative.• Neutrons have no charge.• The cathode ray experiment showed that electrons were negative because they were repelled by a negative plate and attracted by a positive plate.

•The Atomic Nucleus• Rutherford developed an experiment called the Gold- Foil experiment.

• He beamed particles at gold foil. • Some of the particles passed through easily and some were deflected back.

• Some bounced off at large angles.• The nucleus was discovered and that’s what was causing the bounce back of the particles.

• It was also discovered that atoms are mostly empty space.

•Vocabulary Cards• Atom• Proton, neutron, electron (same card)

• Cathode Ray Experiment

• Rutherford Gold- Foil Experiment

•SUM IT UP

Which experiment discovered the atomic nucleus?

•4.3 Distinguishing Among Atoms• Elements are different because they contain different amounts of protons.

• The atomic number of an element is the number of protons.

• The atomic mass number is the number of protons plus the number of neutrons.

•Math Monkey Moment

How many protons, neutrons and electrons are in each atom?

Protons Neutrons

Electrons

Be

Na

Ca

•Isotopes• Isotopes are atoms that have the same number of protons but different numbers of neutrons.

• They have the same atomic number but different atomic mass numbers.

• To distinguish isotopes from each other, writing elements in shorthand notation is necessary.

•Let’s Practice!Write the shorthand notations for:

Oxygen

Sulfur

Silver

Bromine

Lead

Carbon

•Math Monkey Moment

How many protons, neutrons and electrons are in each atom?

Protons Neutrons

Electrons

C-14

Ca-44

Li-7

•Vocabulary Cards

• Isotope

•SUM IT UP

How is an isotope different from a regular atom?

•Atomic Mass• In nature, most elements occur as a mixture of two or more isotopes.

• Each isotope of an element has a fixed mass and a natural percent abundance.

• The atomic mass of an element is the weighted average mass of the atoms in a naturally occurring sample of the element.

• To calculate the atomic mass of an element, multiply the mass of an element by the percent natural abundance and then add the products.

•Math Monkey Moment

Do practice problems 21 and 22 on page 116.

Do practice problems 23 and 24 on page 117.

#21 boron-11

#22 Silicon-28 must be the most abundant. The other two must be present in very small amounts. Silicon-28 has the closest mass to the average atomic mass on the periodic table.

#23 63.6 amu

#24 79.91 amu

•Periodic Table-Preview• A periodic table arranges elements into groups based on a set of repeating properties.

• It allows you to compare the properties of one element with another easily.

• Each horizontal row is called a period.• Each vertical column is called a group.

•Vocabulary Cards• Atomic Mass• Atomic Number• Periodic Table• Table group• Table period

•Science Swag

Research any element from the periodic table.

Write a one page paper about the element. Things you could include are:

Discovery/history

Uses for it now

Future uses

•ANY QUESTIONS?

•POST IT UP

How can you tell which isotope is the most abundant in nature?

I GOT THIS! I NEED HELP!