Ch. 17 – Properties of Atoms and the Periodic Table

Element Symbols a short of abbreviated way to write the name of an element (international system) consist of one capital letter, or a capital letter plus a lower case letter (sometimes 2)

Element Symbol Aluminum Al Calcium Ca Carbon C Chlorine Cl Gold Au Hydrogen H Iron Fe Mercury Hg Nitrogen N Oxygen O Potassium K Sodium Na

Elements and Symbols Need to Know List Calcium Carbon Chlorine Copper Gold Hydrogen Iodine Iron Uranium Mercury Sodium Bromine Oxygen Phosphorus Potassium Silver Sulfur Helium Nitrogen Aluminum

Structure of the Atom Atom- the smallest piece of matter that still retains the properties of the element Each element is made up of only 1 type of atom. Atoms are made of smaller particles called subatomic (smaller than the atom) particles. Subatomic particles – protons, neutrons, and electrons Because subatomic particles are so small, there is a special unit to measure them called the atomic mass unit (amu).

A. The Nucleus The nucleus is the core of the atom. The nucleus is very small -- about a hundred thousand times smaller than the entire atom. However, 99.9% of the mass of the atom is located in the nucleus.

A. The Nucleus Protons and neutrons are found in the nucleus… Protons – positively charged particles All protons are identical, regardless of the atom they are found in. The mass of a proton is 1 amu.

A. The Nucleus Neutrons – electrically neutral particles Neutrons have 0 charge. Just like protons, every neutron is identical. The mass of a neutron is 1 amu.

B. Atomic Number All atoms (elements) are different because they have different numbers of subatomic particles. Specifically, it is the number of protons that determines what the element is. atomic number-the number of protons in the nucleus

B. Atomic Number All hydrogen atoms have 1 proton – their atomic number is 1. All helium atoms have 2 protons – their atomic number is 2. Oxygen = 8 Uranium = 92

D. Atomic Mass (Mass number) Atomic mass-the sum of the number of protons plus the number of neutrons in the nucleus of an atom. *Remember: The nucleus contains most of the mass of the atom (protons and neutrons). The atomic mass can usually be found below the symbol on the periodic table. The units for atomic mass are usually amu.

Mass Number Because they are a measurement, atomic masses are rounded decimals. more specifically: The atomic mass is the average mass of all isotopes of an element. To find the number of neutrons, you subtract the number of protons (atomic number) from the total of protons and neutrons (mass number). Mass number = # p’s + # n’s # n’s = Mass number - # p’s

Examples Carbon Mass #: 12 (#p + #n) Atomic #: 6 (#p) Fluorine Mass number = # p’s + # n’s # n’s = Mass number - # p’s Carbon Mass #: 12 (#p + #n) Atomic #: 6 (#p) # neutrons= 12-6 = 6 C= 6 protons and 6 neutrons Fluorine Mass #: 19 Atomic #: 9 # neutrons= 19-9 = 10 F= 9 protons and 10 neutrons

Examples contd. Iron Mass #= Atomic #= # neutrons = ____-____=_____ Mass number = # p’s + # n’s # n’s = Mass number - # p’s Iron Mass #= Atomic #= # neutrons = ____-____=_____ Fe = ___protons and ___ neutrons Zinc Zn = 30 protons and 35 neutrons

C. Isotopes The atomic number of an element never changes – the number of protons is always constant. However, the number of neutrons is not constant. Isotopes – atoms of the same element with the same number of protons but different numbers of neutrons This means the mass numbers are also different. Isotopes may behave differently than the element itself.

F. Electrons Electrons are subatomic particles with negative charge. Electrons are very small. Their mass is 0.0006 amu. This is about 1/2000th the mass of a proton or neutron. In an uncharged atom, the number of electrons equals the number of protons.

E. Electrons Electrons are located in a fuzzy area around the nucleus called the electron cloud.

E. Electrons Electrons travel around the nucleus billions of times in one second. However, electrons do not travel randomly around the nucleus. Electrons travel in set paths called energy levels (orbitals).

E. Electrons Each level (orbital) can only hold a certain number of electrons until it is full. The arrangement of electrons is what determines whether or not an atom will form bonds to make compounds.

Electron Dot diagrams -show the electrons in an element’s outer energy level (valence electrons) only.

F. Quarks According to current theory, subatomic particles are made of quarks. Every quark has a flavor (6) and color (3).

The Periodic Table Dmitri Mendeleev- Russian chemist who organized the elements by increasing atomic mass in the late 1800s. Periodic- repeated in a pattern Periodic table- the elements are arranged by increasing atomic number and by changes in physical and chemical properties. Henry G.J. Moseley- 1913 –organized the elements according to their increasing atomic numbers.

Groups- elements in the same column (top to bottom) have similar chemical properties. -elements in the same group also have the same number of electrons in their outermost energy level.

Periods- rows of elements. Atomic number increases across a period.