The Atom The atom is the basic unit of matter, everything is made up of atoms. Atoms are very small, and cannot even be seen by a regular microscope. Atoms have no charge (neutral) and are made up of several sub-atomic particles.

Sub – atomic particles: ChargeLocationRelative Mass ELECTRON Negative (-) Orbiting outside nucleus Light PROTONPositive (+) NucleusHeavy NEUTRON NeutralNucleusHeavy

Diagram of the atom:

What makes atoms different from one another? The number of protons, neutrons and electrons an atom has determines what kind of atom it is. Example: The oxygen atom has 8 electrons and protons therefore we know it is an oxygen atom. You can determine the number of electrons and protons an atom has by looking at its atomic number found on the periodic table.

Atomic Number The atomic number of an element is found on the periodic table. They are arranged in increasing order going from left to right. So Hydrogen has an atomic number of 1, Helium is 2 and so on. The atomic number tells us how many protons an atom has. This also tells us how many electrons an atom has, because the number of protons and electrons are balanced. So an atom has the same number of protons as electrons.

To calculate the number of protons and electrons an atom has we must look at the atomic number. Examples: 1.Si 14 electrons, 14 protons 2. Rb 37 electrons, 37 protons 3. Ag 47 electrons, 47 protons 4. N 7 electrons, 7 protons

Isotopes All atoms of the same type would have the same number of protons and electrons, but they don’t have to have the same number of neutrons. Isotope = atoms of the same type, but having different numbers of neutrons, changing the atomic mass.

Atomic Mass The atomic mass on the periodic table a weighted average of the isotopes Atomic mass = #protons + # neutrons # Neutrons = atomic mass - # protons

Example: 1.Na has a mass # of How many e -, p + and neutrons does Na have? e -, p + = – 11 =  12 neutrons

Electron Shells Electrons are found orbiting in shells outside the nucleus Bohr Diagrams are a way to represent where the electrons in an atom are located 1 st shell holds 2 electron 2 nd shell holds 8 electrons 3 rd shell holds 8 electrons 4 th shell holds 18 electrons

Drawing Bohr Diagrams 1.Put the symbol of the element in the centre 2.Start placing electrons in the innermost shells and work outwards 3.Place electrons at N, S, E and W 4.GO back and double if necessary (electrons are usually found in pairs)

Example: Carbon Carbon has an atomic number of 6 Therefore C has 6 electrons 2 electrons in 1 st shell 4 electrons in 2 nd shell

Valence Electrons The outer most electron shell in any atom is called the valence shell The electrons in the valence shell are called Valence Electrons By looking at the number of valence electrons an element has we can predict its reactivity. THE OCTET RULE: Atoms will try to lose, gain or share electrons to obtain a filled outer level (to form a stable octet). Stable octet = 8 electrons

Keeping Track of Electrons The electrons responsible for the chemical properties of atoms are those in the outer energy level.

Keeping Track of Electrons Atoms in the same column have the same valence electrons. Easily found by looking up the group number on the periodic table.

Electron Dot Diagrams An easier way to represent the number of valence electrons an atom has is to use electron dot diagrams. Electron dot diagrams show only the valence electrons

Electron Dot diagrams A way of keeping track of valence electrons. How to write them Write the symbol. Put one dot for each valence electron Don’t pair up until they have to X

The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons. l First we write the symbol. N l Then add 1 electron at a time to each side. l Until they are forced to pair up.

Write the electron dot diagram for Na Mg C O F Ne He

Electron Dots For Cations Metals will have few valence electrons Ca

Electron Dots For Cations Metals will have few valence electrons These will come off Ca

Electron Dots For Cations Metals will have few valence electrons These will come off Forming positive ions Ca +2

Electron Dots For Anions Nonmetals will have many valence electrons. They will gain electrons to fill outer shell. P P -3

Stable Octets All atoms react to achieve noble gas configuration. 8 valence electrons. Also called the octet rule. Ar

Predicting Chemical reactivity: By looking at the number of valence electrons an element has we can predict its reactivity. Atoms will try to lose, gain or share electrons to obtain a filled outer level, or to form a stable octet (8 electrons)

Ions When atoms gain or lose electrons they form something called IONS. Energy is released when this happens. Ions are electrically charged atoms. (positive or negative )

Cations (+) CATIONS: are positively charged ions. Cations are formed when an atom loses electrons. Metals and Hydrogen form cations Ex: Na lose 1 electron  Na 1+

Anions (-) ANIONS: are negatively charged ions. Anions are formed when atoms gain electrons. Most non-metals form anions. Ex: Cl gains one electron  Cl 1-

Trend 4: Ions

You can tell the number of valence electron that an elements has by looking at the group number Group 1 has 1 valence electron Group 2 has 2 Group 13 has 3 Group 14 has 4 Group 15 has 5 Group 16 has 6 Group 17 has 7 Group 18 has 8

Charges of Ions Group 1  loses 1 electron = +1 Group 2  loses 2 electrons = +2 Group 13  loses 3 electrons = +3 Group 15  gains 3 electrons = -3 Group 16  gains 2 electrons = -2 Group 17  gains 1 electron = -1 Group18  has a full outer shell = very stable

Noble Gases Group 8A (He, Ne, Ar, etc.) Have a full valence shell (complete octet) They neither want to gain or lose electrons Therefore, DO NOT form IONS

What kind of ions do the following elements make? (either + or -) a)O b)Br c)Ca d)Se e) Mg f) B g) Cl h) C

What kind of ions do the following elements make? (how many + or -) a)O b)Br c)Ca d)Se e) Mg f) Cl

Answers: a)O (–)h) C can be both (+) (-) b)Br (-) c)Ca (+) d)Se (+) e)Mg (+) f)B (+) g)Cl (-)

Compounds Compound = a pure substance made up of two or more elements that are chemically combined, are neutral Ionic Compounds = substances composed of cations and anions Ionic Bond = the attraction between positive and negative

Making “Ionic Compounds” Activity Groups of 2 or 3 Gather a handful of paper squares Write the symbols for the ions on the squares Positive in one color and Negative in another

Label each of the following on squares: H + Li + Na + K + Be 2+ Mg 2+ Ca 2+ F - Cl - Br - I - O 2- S 2- Se 2- N 3- Fe 2+ Co 3+ Cr 2+ Cu 2+ Al 3+ Ni 2+ P 3- As 3-

The challenge: (only one copy per group needed) By using your paper squares, see how many different combinations your group can make that sum to zero Always write the cation (+) then anion (-) Use subscripts to represent the # of ions Examples: H + Cl -  HCl H + H + O 2-  H 2 O

IONs Summary: Alkali metals form 1+ cations Alkaline earth metals form 2+ cations Noble gases don’t form ions Halogens form 1- anions Group 16 form 2- anions to staircase Group 15 form 3- anions to staircase Transition metals, and metals under staircase, form more than one cation so look at #2 periodic table. (table of ions) ex: Copper can form 2+ and 1+ cations

Ionic Bonding The bond is formed through the transfer of electrons. Electrons are transferred to achieve noble gas configuration. Anions and cations are held together by opposite charges.

Ionic Bonding NaCl

Ionic Bonding Na Cl + -

Counting Electrons During the formation of an ionic compound the total number of electrons lost (by cations) must equal the total number of electrons gained (by anions).

Ionic Bonding All the electrons must be accounted for, total lost = total gained! CaP

Ionic Bonding CaP

Ionic Bonding Ca +2 P

Ionic Bonding Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca

Ionic Bonding Ca +2 P -3 Ca P

Ionic Bonding Ca +2 P -3 Ca +2 P

Ionic Bonding Ca +2 P -3 Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca +2 P -3 Ca +2

Ionic Bonding Ca P P +2 -3

Ionic Bonding Ca 3 P 2 Formula Unit