IONS

SO FAR . . . So far we’ve discussed how to find the number of protons and neutrons in an element. How many electrons do we have in an element? WHAT DO YOU THINK?

ANSWER If an element is neutral (does not have a charge), then the element has the same number of electrons and protons All elements on the Periodic Table are neutral All of the (+) from the protons is cancelled out by the same number of (-) from the electrons

IONS In chemical reactions, atoms often gain or lose electrons (e-) to form charged particles IONS: an atom or group of atoms that has an electric charge because it has lost or gained electrons NOTE: From now on, I will abbreviate (e-) for electrons

VOCABULARY DISTINCTION If an element has the same number of protons and electrons (neutral), it is called an atom atom=neutral If an element has a different number of protons and electrons (has a charge), it is called an ion Ion= have a charge

IONS Atoms start of with a neutral charge In other words, they have the same number of e- and protons Example: Oxygen (O) has an atomic number of 8 This means it has 8 protons Therefore a neutral oxygen atom also has 8 e-

IONS When an atom gains or loses electrons the atom forms a charge Example: Neutral oxygen (O) atom has 8 protons and 8 electrons In a chemical reaction, O gains 2 electrons 8 protons (+) and 10 electrons (-) gives a net (-2) charge

IONS Formula for calculating ion charge: #protons - #electrons = ion charge 8-10=-2 How do we show an ion using a symbol? Neutral atom is the normal atomic symbol For example: Neutral oxygen = O An ion shows the charge associated with the atom For example: Oxygen with a -2 charge = O-2

IONS Calculate the charge on the following ions and write out the ion symbol: Chlorine (Cl) atom with 18 electrons Aluminum (Al) atom with 10 electrons Copper (Cu) atom with 27 electrons Potassium (K) atom with 18 electrons Sulfur (S) atom with 18 electrons

IONS Answers: Cl- Al+3 Cu+2 K+ S-2 NOTE: When an ion has a (+1) or a (-1) charge, we only write a (+) or a (-)

ION TYPES Cation: an ion that has a positive charge Definition of ions Cation: an ion that has a positive charge Anions: an ion that has a negative charge

IONS Ions behave differently than the atoms from which they are formed. Na (neutral sodium)  very reactive and will explode in pure water Na+ (sodium ion)  very stable (is in the table salt we eat) Cations and anions combine together to form neutral compounds

AGAIN, LOOK AT YOUR PERIODIC TABLES Group 1 (alkali metals): lose 1 e- to form (+1) charge Group 2 (alkali earth metals): lose 2 e- to form (+2) charge Group 15 (7A) (halogens): gain 1 e- to form (-1) charge Group 16: gain 2 e- to form (-2) charge Group 15: gain 3 e- to form (-3) charge Transition metals: lose different amounts of e-

HOW DO WE COMBINE THE SYMBOLS FOR IONS AND ISOTOPES Previously, we looked at how to show the symbol for atoms that have a certain number of protons and neutrons Today, we will combine this with the number of electrons also

EXAMPLE How would you write the symbol for an atom that has 29 protons, 34 neutrons and 27 electrons? Step 1: Find the symbol Step 2: Number of protons goes in the bottom left Step 3: Protons + neutrons goes in the upper left Step 4: Charge (protons – electrons) go in the upper right

ANSWER Cu +2 63 29

TRY THESE An atom with 35 protons, 45 neutrons, and 36 electrons. An atom with 12 protons, 13 protons, and 10 electrons. An atom with 10 protons, 10 neutrons and 10 electrons.

TRY THESES Write down the number of protons, neutrons and electrons for the following: 32S-2 16 56Fe+3 26 39K+ 19

Fe+2 Roman Numerals When an element has a Roman Numeral after its name Ex. Iron (II) This is referring to its charge Fe+2