1. Chapter 4: Atoms and Elements Section 3: Subatomic Particles and Elements

2. Learning Goals • Describe the respective properties and charges of electrons, neutrons, and protons. • Determine the atomic symbol and atomic number for an element using the periodic table.

3. Protons • Proton: a positively charged subatomic particle (p) • Located in the nucleus • 1 proton has a charge of +1 • Actual Mass = 1.67262 x 10-27 kg • Relative Mass = 1.0073 atomic mass units (amu)

4. Protons • Elements are defined by their numbers of protons. • If an atom had a different number of protons, it would be a different element. • The number of protons in the nucleus of an atom is its atomic number and is given the symbol Z.

5. Protons • Hydrogen always has 1 proton • Carbon always has 6 protons • How many protons are in: • Argon? • Plutonium?

6. Electrons • Electron: a negatively charged subatomic particle (e-) • Located in the space surrounding the nucleus • 1 electron has a charge of -1 • Actual Mass = 0.00091 x 10-27 kg • Relative Mass = 0.00055 amu • About 1/1840 of the mass of a proton (small enough to be negligible)

8. Electrons • In a neutral atom, the number of electrons is equal to the number of protons. • Hydrogen has 1 electron • Carbon has 6 electrons

9. Electrons • How many electrons are in? • Argon? • Plutonium?

10. Neutrons • Neutron: a subatomic particle that has no charge (n) • Located in the nucleus • Actual Mass = 1.67493 x 10-27 kg • Relative Mass = 1.0087 atomic mass units (amu)

11. Neutrons • The number of neutrons in an atom can vary.

12. Subatomic Particles

13. Electrical Charge • Electrical charge is a fundamental property of protons and electrons. • Positive and negative electrical charges attract each other. • Positive–positive and negative–negative charges repel each other. • Positive and negative charges cancel each other so that a proton and an electron, when paired, are charge-neutral.

15. Electrical Charge • Matter normally has a neutral charge • equal numbers of positive and negative charges that cancel out

16. Electrical Charge • In an electrical storm, the charge balance of matter is disturbed. • The quick rebalancing of charge often occurs in dramatic ways, such as is seen in lightning.

18. Elements • It is the number of protons in the nucleus of an atom that identifies the atom as a particular element.

20. Elements • The periodic table of the elements lists all known elements according to their atomic numbers.

23. Elements • Most chemical symbols are based on the English name of the element. • Hydrogen (H), Carbon (C), Oxygen (O) • Some symbols are based on Latin names. • Potassium (K) – from the Latin kalium • Sodium (Na) – from the Latin natrium

24. Elements • Additional elements with symbols based on their Greek or Latin names include the following: • lead (Pb), mercury (Hg),iron (Fe), silver (Ag), tin (S), copper (Cu)

25. Elements • Early scientists gave newly discovered elements names that reflected their properties: • Argon, from the Greek argos, means “inactive.” • Other elements were named after countries: • Polonium after Poland; Francium after France

26. Elements • Other elements were named after scientists.

27. Elements • Curium is named after Marie Curie, a chemist who helped discover radioactivity and also discovered two new elements. Curie won two Nobel Prizes for her work.

28. Practice • List the atomic symbol and atomic number for each element. • Silicon • Potassium • Gold • Antimony