Unveiling the Nature of Matter: From Atoms to Isotopes

1. The Chemistry of Life • The Nature of Matter • Properties of Water • Carbon Compounds Unit Two History of the Atom Video

2. The Nature of Matter • 2500 years ago Democritus (a Greek philosopher) asked the question: • “If you take an object, like chalk and break it in half, are both halves still chalk?” • Can you continue to divide without limit? • Democritus thought that there had to be a limit, he called the smallest fragment the atom.

3. The nature of Matter • The word atom comes from the Greek word “atomos” , which means “unable to be cut”. • We define an atom as the basic unit of matter. • Atoms are incredible small • Placed side by side, 100 million atoms only make a row about 1 cm long.

4. The nature of Matter Even though atoms are extremely small, they are made up of even smaller subatomic particles! Protons Electrons Neutrons

5. The nature of Matter Protons & Neutrons • Both have about the same mass. • Protons are positively charged particles (+) • Neutrons carry not charge. • Protons and neutrons are held together by strong forces which form the nucleus of the atom.

6. The nature of Matter Electrons: • Has a much smaller mass than protons. • The election is negatively charged (-). • Always in constant motion in the space around the nucleus.

7. The nature of Matter • The number of electrons and protons are always equal. • Their positive and negative charges balance out, so atoms themselves are electrically neutral!

8. The nature of Matter Elements: • An element is a pure substance that consists entirely of one type of atom. • There are over 100 different types of elements; however, only about two dozen are commonly found in living organisms.

9. The nature of Matter Isotopes: • All atoms have the same number of protons and elections • Atoms of an element may have different numbers of neutrons! • Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.

10. The nature of Matter Isotopes: • The total number of protons and neutrons in the nucleus of an atom is called its mass number. • The number of protons in the nucleus of an element is called its atomic number.

11. The nature of Matter Isotopes: • Isotopes are identified by their mass numbers. • The weighted average of an elements isotopes is called the elements atomic mass. • “weighted” means that the abundance of each isotope in nature is considered when the average is calculated.

12. The nature of Matter Isotopes: • Some isotopes are radioactive! • What does radioactive mean? • Their nuclei are unstable and break down at a constant rate over time. • Radioactive isotopes aren’t all bad • Geologists can determine the age of rocks and fossils • Radiation can be used to detect and treat cancer • Some can be used as “tracers” to track the movement of substances in organisms

13. The nature of Matter Chemical Compounds: • In nature, most elements are found combined with other elements. • A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.

14. The nature of Matter Chemical Compounds: • We use chemical/molecular formulas to show the composition of compounds. • H2O Water • NaClSalt • C12H22O11 Sugar

15. The nature of Matter Chemical Compounds: • The physical and chemical properties of compounds are usually very different from those of the elements that make it up. • Hydrogen and Oxygen • Gases at room temperature • Can combine explosively to form liquid water

16. The nature of Matter Chemical Compounds: • The physical and chemical properties of compounds are usually very different from those of the elements that make it up. • Sodium • Silver-colored metal you can cut with a knife • Acts explosively with water • Chlorine • Poisonous yellow-green gas • Used during WWI • Together sodium and chlorine are called sodium chloride which is table salt!

17. The nature of Matter Chemical Compounds: Sodium Metal in Water

18. The nature of Matter Chemical Bonds • Chemical bonds hold the atoms of different compounds together. • Ionic bonds • Covalent bonds

19. The nature of Matter Chemical Bonds • Ionic bonds are formed when one or more electrons are moved, or transferred, from one atom to another. • The atom that loses an electron becomes positively charged. • The atom that gains an election becomes negatively charged. • WHY DO THE CHARGES CHANGE?

20. The nature of Matter Chemical Bonds • Ionic bonds are formed when one or more electrons are moved, or transferred, from one atom to another. • The atom that loses an electron becomes positively charged. • The atom that gains an election becomes negatively charged. • WHY DO THE CHARGES CHANGE?

21. The nature of Matter Chemical Bonds • Ionic bonds: • The positivity and negativity charged atoms are called ions. Oppositely charged ions attract!

22. The nature of Matter Chemical Bonds • In covalent bonds the electrons are shared. • This means the shared electrons travels around the nuclei of both atoms. • Depending on how many electrons are shared will determine what type of covalent bond is formed: • 2 electrons shared = single covalent bond • 4 electrons shared = double covalent bond • 6 electrons shared = triple covalent bond

23. The nature of Matter Chemical Bonds

24. The nature of Matter Chemical Bonds • When atoms are joined by covalent bonds, molecules are formed. • Molecules are the smallest unit of most compounds. • Water molecules form covalent bonds