Chapter 4: Atoms and Elements

 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.

 Proton: a positively charged subatomic particle (p)  Located in the nucleus  1 proton has a charge of +1  Actual Mass = x kg  Relative Mass = atomic mass units (amu)

 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.

 Hydrogen always has 1 proton  Carbon always has 6 protons  How many protons are in:  Argon?  Plutonium?

 Electron: a negatively charged subatomic particle (e - )  Located in the space surrounding the nucleus  1 electron has a charge of -1  Actual Mass = x kg  Relative Mass = amu ▪ About 1/1840 of the mass of a proton (small enough to be negligible)

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

 How many electrons are in?  Argon?  Plutonium?

 Neutron: a subatomic particle that has no charge (n)  Located in the nucleus  Actual Mass = x kg  Relative Mass = atomic mass units (amu)

 The number of neutrons in an atom can vary.

 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.

 Matter normally has a neutral charge  equal numbers of positive and negative charges that cancel out

 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.

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

 The periodic table of the elements lists all known elements according to their atomic numbers.

 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

 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)

 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

 Other elements were named after scientists.

 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.

 List the atomic symbol and atomic number for each element.  Silicon  Potassium  Gold  Antimony