Chapter 10 Atoms & Periodic Table

Chemical symbols - an abbreviated way to write the name of the element. The first letter is capitalized; the second (if present) is lowercase. Latin names are used for many elements so the letters are not always the English initials. Common Symbols: C = Carbon Na = Sodium H = Hydrogen W = Tungsten O = Oxygen Fe = Iron N = Nitrogen Au = Gold 10-1 The Structure of Atoms

Atoms - smallest particle of an element; the basic building blocks of matter. The Parts of an Atom: Nucleus - positively charged center that contains protons and neutrons: the protons have a positive charge: p+ the neutrons have a neutral charge: no charge Electron cloud - surrounds the nucleus and contains electrons which are negative: e-

Atomic number = the number of protons in the nucleus (whole #) and always the same for that element. Mass number = the number of protons PLUS neutrons in the nucleus (whole number); average atomic mass rounded to the nearest WHOLE number. the # of p+ always equals the # of e- in an atom. Descriptive numbers

Relative masses of sub-atomic particles (as compared to each other) amu = atomic mass unit Proton’s mass = 1 amu Neutron’s mass = 1 amu Electron’s mass = amu The mass of an e- is actually 1 / 1840 of the mass of a proton or a neutron.

Atomic Models - used to describe atoms because atoms are so very microscopic. Bohr model - electrons move in definite orbits around the nucleus. Electron cloud model - e- move in regions around the nucleus in “energy levels”. This model is most widely accepted. Relative size of electron and nucleus If the electron cloud were the size of a pro football stadium, the nucleus would be the size of a golf ball.. Ex: the nucleus: golf ball, the e-cloud: stadium Atomic Models

10- 2 The Electron Cloud The electron cloud is NOT the exact location of each electron, just the probable location or area where it moves. The electrons move around the nucleus in “energy levels”. The electrons in the energy levels closer to the nucleus have less energy than the electrons that are farther from the nucleus. Energy levels (n) have a maximum number of e- they can hold. 1st level can hold 2 e- use the 2(n)² formula 2nd level up to 8 e- 3rd level up to 18 e- 4th level up to 32 e-

10-2 Smaller Particles of Matter Quarks - are the smaller particles of matter that make up protons and neutrons. *One arrangement of 3 types of quarks forms a neutron. *Another arrangement of 3 different quarks forms a proton. A supercollider is used to accelerate protons in order to study collisions that can help reveal information about the inner structure of the atom. Masses of Atoms Atomic mass - the relative mass of an atom; based upon an atomic mass unit; compared to carbon-12. Atomic mass unit is 1/12 the mass of a carbon-12 atom. Mass number - the sum of the protons & neutrons in an atom.

Isotopes - atoms of the same element with different numbers of neutrons (same # of protons); less common than the main element. The existence of isotopes accounts for the average atomic mass. Average atomic mass - the average mass of the mixture of an element & its isotopes; only a whole number if radioactive or man-made; usually carried to 2 or 3 places past the decimal. The # of protons determines what the element is; the # of neutrons determines the isotope of that element Masses of Atoms

The Periodic Table - arrangement of elements according to repeated changes in properties. Dimitri Mendeleev (Russian, 1800's) arranged all the elements known at that time, in order of increasing atomic masses & discovered a repeating pattern of properties or characteristics. ***There were some gaps in masses so he placed question marks in their spots. Later, elements were discovered to fill in these gaps. His predictions about elements, their masses & properties proved to be true.*** Henry Moseley arranged the elements by increasing atomic number. This is the form of periodic table that we use today The Periodic Table

The Periodic Table

Groups or Families of Elements Groups or Families of Elements - the vertical columns on the table, numbers 1 thru 18 Elements in the same group/family have similar properties such as the # of electrons in their outer shell or energy level. Electron dot diagrams were developed using the symbol and “dots” to represent the electrons in the outer energy level. (see pg 260.) Each group or “vertical” column has a specific number of e- in the outer shell. The last column has eight. Periods are the “horizontal” rows. Each row indicates the number of “energy levels” or shells in the atom.

Metals – located on the left side of the chart; most are solids, are shiny & good conductors of heat & electricity. Transition elements – located in groups 3 thru 12; have metallic properties. Metalloids - have properties of metals & nonmetals; found along the zig-zag line or the “staircase” of the chart. Non-metals – located on the right side of chart; usually gases or brittle solids; not good conductors. Groups of elements