Electrons Valence electrons are important in deciding which atoms can bond (chemically combine to form a new substance) All atoms want to have 8 valence electrons. The only exceptions are H and He. Hydrogen and Helium only want 2 valence electrons.
Compounds Elements combine with other elements to get the 2 or 8 valence electrons. When two elements chemically combine to form something new the result is called a chemical compound. When a compound is formed people say a bond was formed between the elements.
Compounds When two or more elements combine or exchange valence electrons they bond or form a molecule This is a chemical change because a new substance is formed. You can see compounds form in chemical reactions or changes.
Learning Launch Turn in homework to box (purple sheet) AND get out periodic table LL 10/11/2013 Get out notes from yesterday (white sheet) Find the number of Find the number of Find the number of Protons for… Neutrons for… Electrons for… Xe _______He _________O _______ K _______Si _________Cl _______ Fe _______I __________B _______ Ne _______Mg ________Na ______
So how and why do these electrons move? 1.The nucleus (center) of the atom is surrounded by swirling electrons. 2. The electrons move on invisible rings called energy levels, orbitals or shells.
Lets look Each orbital or energy level can only hold a certain number of electrons… 3. The first energy level around the nucleus can only hold a maximum of 2 electrons… it is not strong enough to hold anymore…
4. Which elements on the periodic table only have 1 or 2 total electrons? Hydrogen and Helium REMEMBER!!! Atomic number = number of protons = number of electrons So.. You look at the top number to find the total number of electrons in 1 atom of that element… and the answer to our question is…
They look like this. Hydrogen (H)Helium (He) Atomic Number - 1Atomic number - 2 1 electron2 electrons
Lets fill in some info Hydrogen Atomic number: __1___ Has __1____ electron and __1____ proton. In Group/Family number_1__ In Period: __1___ Has ___1___ energy level Helium Atomic number: ___2___ Has __2___ electrons and ___2___ protons. In Group/ Family number __18__ In period _____1___ Has ___1_____ energy level.
What next… 7. Once the first energy level has two electrons on it, it is full, so if an atom has more than 2 electrons, it needs another energy level… Lets look at Lithium. Lithium – atomic # 3
Lithium Lithium has an atomic number of.. That means that is has protons and electrons. Can all of Lithium’s electrons fit on one energy level?? NOOOOO!
Because the first energy level can only hold a max. of 2 electrons… An atom of Lithium (Li) must have two energy levels to fit all 3 electrons. It looks like this
Fill in info on Lithium Atomic number: __3__ Has __3____ electrons and __3____ protons. In Group/Family number_1__ Has _1____ valence electron In Period: __2___ Has _2___ energy level