Chemistry 101 Chapter #4: Atoms and Elements

Chemical Symbols

1 or 2 letter abbreviations for the names of the elements Only the first letter of an element's symbol in capitalized; if there is a second letter, it is lowercase Example C = Carbon Co = Cobalt

J. J. Thomson (1897)

Applied electricity to a glass tube and produced streams of small particles called cathode rays The rays were attracted to a positively charged electrode He reasoned that the particles in the cathode ray must be negatively charged, called them electrons Further experiments showed that the electrons were much smaller than the atom and had extremely small masses Proposed the "plum pudding" model of an atom, according to which protons and electrons are distributed throughout the atom Pudding = PROTONS Plum = ELECTRONS

Periodic Table

Arrangement of the 118 elements by increasing atomic number such that elements having similar chemical behavior are grouped in vertical columns Created by Dmitri Mendeleev - 1872

Isotope

Atoms of the same element that have the same atomic number but different number of neutrons Explanation: different mass numbers

James Chadwick (1932)

Discovered that the nucleus of the atom also contained neutral particles called neutrons

Mass Number

Equal to the number of protons + the number of neutrons Represents the number of particles in the nucleus Does not appear on the periodic table because it applies to a single atom only Mass Number = Number of protons + number of neutrons Number of neutrons = Mass Number - Number of protons

Atomic Number

Equal to the number of protons in an atom (and electrons) Specific for each element and the same for all atoms of that element Appears above the symbol of an element Atoms are electrically neutral; Net charge of 0 = Number of PROTONS = Number of ELECTRONS

Alkali Metals

Group 1A (1) Li, Na, K, Rb, Cs, and Fr (NOT HYDROGEN) Soft shiny metals Good heat and electricity conductors Relatively low melting points React vigorously with water

Alkaline Earth Metals

Group 2A (2) Be, Mg, Ca, Sr, Ba, and Ra Shiny metals Not very reactive

Halogens

Group 7A (17) F, Cl, Br, I, and At Highly reactive Forms compounds with most elements

Noble Gases

Group 8A (18) He, Ne, Ar, Kr, Xe, and Rn Very non-reactive Seldom found in combination with other elements

Representative Elements

Group numbers 1A to 8A

Transition Elements

Group numbers followed by the letter "B"

No Common Names

Groups 3A (13), 4A (14), 5A (15), and 6A (16)

Period

Horizontal ROW (1 - 7) Period 1 contains two elements: H and He Periods 2 and 3 each contain eight elements: Period 2 - Li, Be, B, C, N, O, F, He Period 3 - Na, Mg, Al, Si, P, S, Cl, Ar

Metalloids

Include B, Si, Ge, As, Sb, Te, Po, and At All the elements along the zigzag line are metalloids except for aluminum (Al) Metalloids are: Exhibit some properties typical of metals and some typical of nonmetals Better conductors of heat and electricity than nonmetals, but not as good as metals Semiconductors because they can be modified to function as conductors or insulators

Nonmetals

Include elements such as hydrogen (H), carbon (C), nitrogen (N), oxygen (O), chlorine (Cl), and sulfur (S) Nonmetals are: Not especially shiny, malleable, or ductile and are often poor conductors of heat and electricity Typically have low melting points and low densities

Metals

Includes copper (Cu), gold (Au), and silver (Ag) Metals are: Shiny solids Ductile, meaning they can be shaped into wires Malleable, meaning they can be hammered into a flat sheet Good conductors of electricity Melted at much higher temperatures than nonmetals Solids at room temperature, except for mercury (Hg), which is a liquid

Subatomic Particle

Includes protons, neutrons, and electrons

Atomic Symbol

Indicates mass number in the upper left corner and the atomic number in the lower left corner Represents a particular isotope of an element

Dalton's Atomic Theory

John Dalton (1766-1844) developed an atomic theory proposing that atoms were responsible for the combinations of elements in compounds The idea of atoms did not become scientific theory until 1808 Theory: All matter is made up of tiny particles called atoms All atoms of a given element are identical to one another and different from atoms of other elements (We now know that the atoms are not identical but similar, and that they are made up of subatomic particles) Atoms of two or more different elements combine to form compounds (A particular compound is always made up of the same kinds of atoms and the same number of each kind of atom) A chemical reaction involves the rearrangement, separation, or combination of atoms (Atoms are never created or destroyed in a chemical reaction)

Calculating Atomic Mass

Multiply the mass of each isotope and the percentage abundance mass isotope (1) × (%)/100 + mass isotope (2) × (%)/100 ---------------------------------- atomic mass of element

Electron

Negatively charged subatomic particle Smaller mass than protons and neutrons

Neutron

Neutral subatomic particle having a mass about 1 amu; Found in the nucleus of an atom

Proton

Positively charged subatomic particle They are much heavier than electrons

Nucleus

Small region in the center with positive charge (contains protons and neutrons)

Atom

Smallest particle of an element that retains the characteristics of the element All elements listed on the periodic table are made up of these Atoms are the building blocks of everything around us; Too small to see with the naked eye

Atomic Mass Unit (amu)

Units that chemists use; Defined as one-twelfth of the mass of the carbon atom with 6 protons and 6 neutrons

Group

Vertical COLUMN

Atomic Mass

Weighted average mass of all the naturally occurring isotopes of an element Listed below the symbol of each element on the periodic table Not the same as the mass number

Ernest Rutherford (1911)

Worked with J. J. Thomson and developed a new structure for the atom based on Rutherford's gold foil experiments From his gold foil experiments, Rutherford determined that atoms contained a nucleus A region of space around the center that was occupied by electrons The particles that hit the nuclei deflected, the ones that didn't hit the nuclei passed through the area with the electrons

Group Number

Written at the top of each vertical column