On Earth, ____ elements occur naturally.

Which of the following does not occur naturally on Earth?

Which scientist created the periodic table of elements?

The _____________ organizes the elements into a grid of horizontal rows called periods and vertical columns called groups.

The table is called "___________" because the pattern of similar properties repeats as you move from period to period.

You know that _______ is classified as pure substances and mixtures.

A ____________ mixture is one that does not blend smoothly throughout and in which the individual substances remain distinct.

Homogeneous mixtures are also referred to as ______

Today, there are approximately _____ million known compounds, and new compounds continue to be developed and discovered at the rate of 100,000 per year.

A physical change alters the composition of a substance.

A substance is a form of matter with a uniform and unchanging composition.

Physical properties can be observed without altering a substance's composition.

Only physical properties are affected by external conditions such as temperature and pressure.

A mixture is a physical blend of two or more pure substances in any proportion.