Chemistry

4. a chemical substance that is present at the start of a chemical reaction
7. chemical equation with the same number of atoms of each element on both sides of the equation
8. formed when atoms share electrons - nonmetals form covalent bonds
10. a mixture that is the same throughout
11. any compound that increases the number of hydrogen when dissolved in water
13. any of the more than 100 known substances that cannot be separated into simpler substances and that singly or in combination make all matter
15. a combustion reaction is when oxygen combines with another compound to form water and carbon dioxide
17. a change in which one or more substances combine or break apart to form new substances
19. a substance made up of atoms of two or more different elements joined by chemical bonds
20. a substance that decreases the hydrogen ion concentration in a solution

1. the simplest structural unit of an element or compound
2. a type of mixture in which the parts of the mixture are noticeably different from one another
3. the number placed in front of a chemical symbol to balance the equation
5. a chemical substance formed as a result of a chemical reaction
6. anything that has mass and occupies space
9. characteristics that can only be observed when one substance changes into a different substance
12. the smallest component of an element having the chemical properties of the element
14. a chemical bond resulting from the attraction between oppositely charged ions
16. the amount of matter in an object
18. a solution with a pH of 7