Molecules, Compounds, and Pure Substances

Molecules, Compounds, and Pure Substances

Week 5 Quarter 3

VOCABULARY ALERT

molecule – the simplest form of a chemical compound that can exist, formed when two or more atoms join together chemically

Combining Atoms

A pure substance made up of many atoms with the same atomic number is called an element. Atoms can exist by themselves (ex: helium gas) or combine to form a molecule with the same type of atom (ex: hydrogen gas).

Combining Atoms

Atoms can also combine (bond) with different kinds of atoms to form molecules of pure substances called compounds (ex: water).

Multiple Choice

Compounds are when two different types of atoms come together to form a new pure substance.

• agree

• disagree

Combining Atoms

There are equations for describing the chemical and physical reactions that can form compounds. Chemical letter symbols are used for each element in a molecular formula.

Multiple Choice

All molecules are compounds.

• agree

• disagree

Names and formulas

Compounds are assigned special chemical names, a common name if the substance is well known, and a formula. This information reveals its chemical structure. For example, eggshells are made of the chemical substance calcium carbonate, written as the formula CaCO3 .The formula, CaCO3 , means every molecule of eggshell has one calcium atom (Ca), one carbon atom (C), and three oxygen atoms (O). 

VOCABULARY ALERT

A pure substance is a single substance, either an element or a compound, with a definite structure and set of chemical and physical properties.

Pure Substances and Their Structure

Individual atoms of the same type connected to form an extended structure

Pure Substances and Their Structure

Solids made up of two atoms of different elements that then connect to form extended crystalline structures

Pure Substances and Their Structure

Individual atoms that are not attracted to each other

Pure Substance and Their Structure

Molecules of different types of atoms that are not attracted to each other.

Pure Substances and Their Structure

Molecules composed of four different types of atoms that are attracted to each other to form extended structures.

Pure Substances and Their Structure

Diatomic (two) molecules of the same type of atom that are not attracted to each other.

VOCABULARY ALERT

A compound is two or more different atoms bonded together

Compounds

Just because two compounds have the same elements does not mean they are the same substance. Look at the compounds on the side. The one on the left is water. On the right is hydrogen peroxide, the bubbly stuff you apply to cuts. They both have hydrogen and oxygen, but in different ratios.

Compound Structure

Water has two hydrogen atoms and one oxygen atom, and hydrogen peroxide has one hydrogen per each oxygen. Different models reveal different structural information. There are many different ways to model a compound.

Crystal Structure

The structure of solid matter can be either disordered or ordered. In some types of substances, the molecules or atoms arrange themselves into neat, ordered patterns called a crystalline lattice, which is what causes crystals to form. In other instances, there is no order. In the unordered solids, there is no pattern; the atoms are disordered, or amorphous.

Multiple Choice

Atoms that have no specific arrangement and that are considered disordered are still considered solid matter.

• agree

• disagree

Open Ended

What questions do you still have about molecules, compounds, or pure substances?

Open Ended

Write 2-3 things you want to remember about molecules, compounds, or pure substances.