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Atomic Structure 3.1 Atomic History •In 400 BC a Greek Philosopher, Democritus suggested the universe was made of invisible units--atoms. 1800’s John Dalton’s Theory (Still Accepted) 1. Every element is made of tiny, unique particles called atoms 2. Atoms of different elements can join to form molecules. John Dalton’s Theory- Disproved 3. Atoms are the smallest particles and cannot be subdivided. 4. Atoms of the same element are exactly alike in mass JJ Thomson Credited with discovering negative charged particles called electrons. Rutherford Credited with discovering nucleus. and atoms are mostly empty space. http://micro.magnet.fsu.edu/electromag/java/rutherford/ Further Research Finding Later on, the discovery of protons and neutrons were discovered in the nucleus. And it was later concluded that all atoms are neutral in charge. The number of protons and electrons in any atom are always equal. Niels Bohr Suggested that electrons move around atoms in set paths around the nucleus. He said each path is an energy level STOP Today’s Theory It is impossible to pinpoint an electron’s exact position due to its tremendous speed. Electrons do not move around in definite paths. Today’s Theory Electrons are found in orbitals within energy levels. (s, p, d, and f ) a region in an atom where there is a high probability of finding electrons. Today’s Theory Electrons are now viewed as waves vibrating on a string rather than simple particles. Wave-Particle Duality Theory What are atoms? The smallest part of an element that still has the element’s properties. Parts of an atom Nucleus Proton Neutron Electron Subatomic particles Nucleus •center of an atom •positively charged •makes up 99.9% of the atom’s mass •contains protons and neutrons Protons Charge (+) Mass is equal to 1 atomic mass unit (amu) Found in the nucleus Identifies the element/atom Neutrons Charge (0) – neutral Mass is equal to 1amu Found in the nucleus Helps determine mass Electrons •Charge is negative (-) •Mass is equal to 0 amu •Found outside the nucleus, in the electron cloud Energy levels 1st level holds up to 2 e2nd level holds up to 8 e3rd level holds up to 8 or 18 e4th level holds up to 8, 18, or 32 eOuter Level holds up to 8 e(called valence electrons) Valence Electron The number of electrons in the outermost electron shell. Most important A Guided Tour of the Periodic Table 3.2 Periodic Law •Properties of elements tend to change in a regular pattern when elements are arranged in order of increasing atomic number. Periodic Law Periodic Table is set up by increasing atomic number. Atomic Number is the # of protons in the atom. Average Atomic Mass Atomic Number •tells you number of protons •Never Changes for an atom. •Appears as a whole # on the periodic table. •No two elements can have same atomic #. Atomic Number Atomic Number # of protons Mass Number The mass of an atom Total number of protons plus neutrons in the nucleus of a single atom. Atoms of the same element won’t always have the same mass number Mass Number # of protons # of neutrons Mass # Isotopes •Any atoms having the same number of protons but different number of neutrons. •So they also have different mass numbers. Average Atomic Mass Average mass of all known isotopes for an element Found on the periodic table as a number with a decimal Atom’s Charge •They are neutral. •All atoms have the same number of protons and electrons. •Charges cancel each other out. Ions Charged particles. Form when atoms lose or gain electrons. They do this so the ions have a full outer shell Two Types. Cations •Positively charged ions. •Form when atoms lose electrons. •Metals •Left side of table Cations # of protons greater than # of electrons More (+) than (-) Na Atom + Na Cation Anions •Negatively charged ions. •Form when atoms gain electrons. •Nonmetals •Right side of table Anions # of protons less than # of electrons More (-) than (+) Cl Cl atom Anion Quantifying atoms or ions +1 Protons = 3 Neutrons = 7-3 = 4 Electrons = 3 Electrons = 3 -1 = 2 Families of Elements 3.3 Periodic Table Periods -a horizontal row of elements. -Tells you the electrons energy level. Periodic Table Groups (families) -a vertical column of elements. -Tells us the # of valence electrons and the elements’ chemical properties. Types of Elements 1. Metals 2. Nonmetals 3. Semiconductors/metalloid Transition Metals Inner Transition Metals Alkali Metals Group 1 Most reactive metals one valence eFound as compounds (salts) and not elements due to reactivity. As elements they are soft metals and good conductors. fun Alkaline-earth Metals Group 2 Less reactive than Alkali They are also more commonly found as compounds 2 most common are Ca and Mg. Transition Metals Groups 3-12 Less reactive than groups 1 and 2 Good conductors Transition Metals All solids with the exception of mercury Valuable metals (Ag, Au, Pt, Cu, Ni, Fe, Co) Non Metals Are not able to conduct electricity or heat very well. Found in groups 13-18, with the exception of hydrogen Carbon Found as an element (coal, diamond, graphite) Found in millions of different compounds Called Organic Compounds HYDROGEN It is a gas/nonmetal A very explosive gas. It is located in group one because it has one valence electron http://www.youtube.com/watch?v=KLzY88uHFn0 Oxygen and Nitrogen Oxygen is the most common element found on Earth Nitrogen most common gas found in the atmosphere Halogens Group 17 Most reactive nonmetals Form salts with group 1 Used to kill bacteria Bromine only liquid nonmetal Noble Gases Group 18 Stable and not reactive. (inert) Don’t form compounds. They have a full valence shell. Metalloids (Semiconductors) 7 elements on the step Properties of both metals and nonmetals. Silicon the most familiar (computer chips) Inner Transition Metals Two rows at the bottom Some are Radioactive ex. Uranium 93 and greater are all manmade
