How are the elements on the periodic table organized?

Bellwork: Friday, September 21st

Elements & Compounds

Chapter 3.4

Dmitri Mendeleev first began to organize the elements by similarities in mass.◦ He was the first one to create a periodic table,

though we no longer organize it by atomic mass

Periodic Table: History

Arrange by atomic number (number of protons)

Organizes elements into a grid of horizontal rows called periods and vertical columns called groups or families

Elements in the same group have similar chemical and physical properties

Periodic Table Today

Elements- pure substances that cannot be separated into simpler substances by physical or chemical means◦92 naturally occurring ◦Others have been developed by scientists (synthetic)

◦Not equally abundant Examples: 75% of universe is hydrogen

and oxygen, carbon, and hydrogen make up 90% of the human body and francium is the least abundant element with only 20g total in the Earth’s crust

◦Each has a unique chemical name and symbol

Symbols are 1, 2, or 3 letters

First letter is ALWAYS capitalized

Remaining letters are ALWAYS lowercase

Universally accepted system so that scientists can communicate

Element Symbols

4-5 quizzes◦ 3 announced◦ 1-2 unannounced

Quiz Monday, 24th (Actinium –Hydrogen)

Quiz Wednesday, 26th (Iodine-potassium)

Quiz Friday, 28th (Radium-Zirconium)

What elements do YOU need to know?

Made up of 2 or more different elements that are chemically combined◦ Most matter exists in this form◦ 10 million known compounds◦ New ones are created at a rate of

100,000/year◦ Can be broken down into simpler

substances by chemical means◦ More stable than individual

elements

Compounds

Coefficient: A number that comes in front of a chemical formula, indicates how many molecules of that compound you have.◦ Examples: 4CO2 3H2O

Subscripts: a number that is below the elements listed in the compound, indicates how many of each element you have.◦ These numbers only apply to the number in

FRONT of them.

◦ Examples: 4CO2 3H2O

Identifying the number of atoms in a compound:

Figure out how many atoms are in each compound!

Let’s Practice!

Determine how many atoms are present in the following compounds:

◦1. H3PO4

◦2. NH4H2PO4

◦3. 3CaCrO4

◦4. 4K2Cr2O7

Bellwork: Monday, September 24th

A compound is always composed of the same elements in the same proportion by mass◦ The same amounts of the elements in a

compound can be expressed by percent mass

x 100

Law of Definite Proportions

A 200.0g sample of sugarcane contains 32.5g of hydrogen. What is the percent by mass of hydrogen in the compound?

Example Problem:

The same elements can form more than one compound ◦ Happens if different compounds have different

mass compositions Example: Water and Hydrogen Peroxide

Mass ratio of compound I Mass ratio of compound II

*Look at the example on page 89*

Law of Multiple Proportions

Chapter 3 pg 977: 1-4

Practice Problems: 19-22 pg 88

Practice Problems: 28-29 pg 90

Homework