Atoms, Molecules, & Compounds

All the elements that naturally are found on Earth come from...

• Stars exploding and "dying" (novae or super novae!)

• The Moon

• The formation of stars

• The Big Bang

True or False: Helium (He) can be found in the Earth's atmosphere.

• True

• False

The number 2 in H₂O tells you that each unit of the compound contains two ___________ atoms.

• Hydrogen

• water

• Oxygen

• elements

The total number of atoms in Fe₂O₃ is

• two

• five

• six

• three

A ______ can have the same or different atoms chemically bonded to each other.

• compound

• molecule

A _______ is a molecule that has different atoms chemically bonded to each other.

• compound

• molecule

Which of the following is a compound?

• H₂

• He₂

• H₂O

• O₂

The atoms in a molecule are held together by

• gravitational attraction
• chemical bonds
• frictional forces
• physical bonds

Chemical bond always involves which part of the atom?

• protons

• neutrons

• electrons

• nucleus

A covalent bond is when two atoms __________ electrons.

• fight over

• share

• transfer

• exchange