ATOMS AND THE PERIODIC TABLE CHAPTER 4 Meet

ATOMS AND THE PERIODIC TABLE CHAPTER 4 Meet the Elements

VOCABULARY --REVIEW and INTRODUCTION l Atoms – smallest part of an element that still retains all properties of that element. – – l l Atoms can be broken down into subatomic particles. Atoms can combine to form molecules. Molecule – the smallest part of a compound that still retains all properties of that compound. ELEMENTS, ATOMS, MOLECULES, COMPOUNDS

Subatomic Particles l Nucleus – center of atom – – l Neutrons – no charge Protons – positive charge Energy Levels – located around nucleus – Electrons – negative charge l Electrons move in a cloud around the nucleus

Atomic Models l Bohr’s Model (1913) – – Niels Bohr suggested electrons moved in orbits around the nucleus … similar to planets moving around the sun. Each electron could only move in specific orbits or paths.

Atomic Models l 1925 – Electron Cloud Model – – – Electrons move in a region or general area surrounding the nucleus. (called an electron cloud) An electrons exact speed, direction or location cannot be determined at any one particular moment. Electrons are located at various distances around the nucleus l l Electrons close to the nucleus have LOW energy Electrons far away from the nucleus have HIGH energy

Electron Cloud Model l l l Electrons exist in energy levels The number of energy levels that are filled will depend on the number of electrons of that atom. 1 st energy level holds 2 electrons 2 nd energy level – 8 electrons 3 rd energy level – 18 electrons 4 th energy level – 32 electrons

Electron Cloud Model l Octet Rule – An atom is considered stable (happy) when its outer energy level is full of electrons. (8 outer electrons is considered stable). l Valence Electrons – Electrons found in the outermost shell of an atom – – Valence Electrons determine the chemical properties of an atom. When valence shell is not full…the atom will be more reactive

Dot Diagrams (Lewis Structure) and Valence Electrons l Uses the symbol of the element and dots to represent the electron in the outer energy level

Periodic Table Element Song

Dmitri Mendeleev: Father of the Periodic Table l l HOW HIS WORKED… Put elements in rows by increasing atomic weight. Put elements in columns by the way they reacted. l l SOME PROBLEMS… He left blank spaces for what he said were undiscovered elements. (Turned out he was right!) He broke the pattern of increasing atomic weight to keep similar reacting elements together.

The Current Periodic Table l l Mendeleev wasn’t too far off. Now the elements are put in rows by increasing ATOMIC NUMBER!!

Periodic Table l l The arrangement of elements according to repeating changes in properties Each box on the periodic chart contain the atomic number, chemical symbol, name, and average atomic mass.

Periodic Table Organization l Groups – A vertical Column of elements – – l Elements in the same group have the same number of valence electrons. Elements of the same group have similar chemical properties. Periods – Horizontal Rows – The number of protons increase by one from left to right (so do # of electrons)

Periodic Table Organization l l l Chemical Symbol – Abbreviated way to write the name of the element (EX: O – Oxygen) Atomic Number – The number of protons in the nucleus Atomic Mass Number – The number of protons plus neutrons in the nucleus (often a decimal number) – – This number may be rounded…round up if it is. 5 or above and down if. 4 or below) The mass number is an AVERAGE

Ions and Isotopes l Ions – An atom or group of atoms that has lost or gained one or more electrons and has a negative or positive charge – – Occurs when an atom gives up an electron or takes an electron because outer energy levels are not full CATION – positive ion (loses electrons and becomes positive) ANION – negative ion (gains electrons and becomes negative) (pictures)

Ions and Isotopes l Isotopes – An atom that has the same number of protons as other atoms of the same element do but has a different number of neutrons. – Isotopes are often radioactive l – Used for cancer treatments, preserving foods, etc. Example: Hydrogen has three isotopes l Protium, Deuterium, Tritium

Isotopes of Hydrogen and Carbon

Families of Elements l l Members of a family in the periodic table have many chemical and physical properties in common…they have similar valence electrons. 3 Groups: – Metals, Nonmetals, Semiconductors – The Periodic Table of Videos - University of Nottingham

Hydrogen l l Hydrogen belongs to a family of its own. Hydrogen is a diatomic, reactive gas. Hydrogen was involved in the explosion of the Hindenberg. Hydrogen is promising as an alternative fuel source for automobiles

Metals l l Four different kinds of metals Share common properties of: existing as solids at room temperature, shiny, good conductors of heat and electricity

1. Alkali Metals l l l Group 1 Very Reactive…Have only 1 valence electron Always combined with something else in nature. – Example: Sodium must be stored in oil so as not to react with moisture in air.

2. Alkaline-Earth Metals l l l Located in Group 2 Have 2 valence electrons Less reactive than Alkali Metals Always combined with nonmetals in nature Ex: Calcium and Magnesium

3. Transitional Metals l l Groups 3 -12 Much less reactive These elements properties gradually change from being more similar to Group 2 to being more similar to Group 13 as you move from left to right Examples: Gold, Platinum, Silver

4. Synthetic Elements l l All elements above #92 are man-made Many are radioactive

Nonmetals l l Located on the right side of the periodic table Includes some elements in Groups 13 -16 and all elements in Groups 17 -18 Plentiful on Earth 3 Groups

1. Halogens l l l Group 17 Very Reactive Always combined with another element in nature Has 7 valence electrons Used as disinfectants and to strengthen teeth

2. Noble Gases l l l Group 18 Unreactive; Do not make compounds with anything. 8 Valence Electrons (full outer energy level)

3. Semiconductors (Metalloids) l l l Intermediate conductors of heat and electricity Includes 6 elements Located on the “stairstep line” – Includes: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium

Diatomic Molecules l If these elements are found alone in nature they are always bonded to themselves because they are very reactive. – l Example: O 2, H 2, Fl 2, Br 2, I 2, N 2, Cl 2 There are 7 – Including: Hydrogen, Oxygen, Fluorine, Bromine, Iodine, Nitrogen, Chlorine