 The basic unit of an element that can retain the properties of that element in a chemical reaction

1. Protons (P+) 2. Neutrons (N 0 ) 3. Electrons (e - )  Aka:  Subatomic Particles

Subatomic Particle SymbolLocationRelative Mass Charge ProtonP+Nucleus1 amu+1 NeutronN0N0 Nucleus1 amu0 Electrone-Electron cloud 0

 Changing the # of protons changes the identity of the element  Changing the # of neutrons change the mass of the atom  Changing the number of electrons changes the charge of the atom

Since like charges repel, how does the nucleus stay together?

Strong forces in the nucleus

 Atomic Number  Tells us how many protons are in the nucleus of each atom of an element  Represented by the letter Z

 What is the atomic number of carbon?  How many protons are in the nucleus of a carbon atom?

 What is the atomic number of carbon?  6  How many protons are in the nucleus of a carbon atom?  6

 Mass Number  Tells us the number of protons and neutrons in the nucleus of each atom of an element  Represented by the letter A

 Shorthand Notation:  Element name – mass number  Ex: carbon–12, carbon-14, chlorine-35  12, 14, 35 = mass # (protons + neutrons)

 Shorthand Notation:  AZX notation:  X =Element Symbol  A =Mass Number  Z =Atomic Number  Ex: Chlorine-35  Cl always has 17 p+

 What is the mass number of carbon-12?  How many neutrons are in the nucleus of a carbon-12 atom?

 What is the mass number of carbon-12?  12  How many neutrons are in the nucleus of a carbon-12 atom? = 6 Mass # # P+  Mass number = # of protons + # of neutrons  Mass # = Atomic # + # of neutrons  Number of neutrons = Mass # - Atomic #

 In a neutral atom, the number of electrons equal the number of protons  Neutral:  0 charge (so # of negative charges (e-) = # of positive charges (P+)

 Isotopes are atoms of the same element that have a different number of neutrons.  Changing the number of neutrons will change the mass number

 Ex: Carbon-11 Carbon-12 Carbon-13 Carbon-14  Ex: 11 6 C 12 6 C 13 6 C 14 6 C  *Notice that all carbon isotopes have an atomic number (#of protons) of 6. The number of neutrons change so the mass will change*

 Single atom extremely small  Ex: Fluorine atom mass = 3.155x  More convenient to compare relative masses of atoms using a reference isotope as a standard  Chosen reference isotope is carbon-12  Carbon-12 has atomic mass of exactly 12 atomic mass units  What is the atomic mass of carbon?  What is the atomic mass of chlorine?

 Single atom extremely small  Ex: Fluorine atom mass = 3.155*  More convenient to compare relative masses of atoms using a reference isotope as a standard  Chosen reference isotope is carbon-12  Carbon-12 has atomic mass of exactly 12 atomic mass units  1 atomic mass unit (amu) = 1/12 mass of carbon-12  What is the atomic mass of carbon?  What is the atomic mass of chlorine? 35.45

 Bottom Line: The atomic mass is a weighted average of the masses of an element’s isotope

 Use a weighted average  Formula: (mass 1)(%abundance 1)+(mass2)(%abundance 2) +… **% abundances should be in decimal form** (take your percentage & divide by 100)

 Formula: (mass 1)(%abundance 1)+(mass2)(%abundance 2) +… **% abundances should be in decimal form** (take your percentage & divide by 100)  Ex: Boron forms 2 stable isotopes, boron-10 and boron-11. The relative abundance of the isotope are 19.8% and 80.2% respectively. What is the atomic mass?

 Formula: (mass 1)(%abundance 1)+(mass2)(%abundance 2) +… **% abundances should be in decimal form** (take your percentage & divide by 100)  Ex: Boron forms 2 stable isotopes, boron-10 and boron-11. The relative abundance of the isotope are 19.8% and 80.2% respectively. What is the atomic mass? (10amu)(.198) + (11amu)(.802) = amu Check yourself: Atomic # should match periodic table

 An ion is an atom or group of atoms that has a charge  A neutral atom has equal numbers of protons and electrons  Ions form as atoms gain or lose electrons  Don’t mess with the protons!!

 Examples 7 3 Li O Mg 2+ Protons- 12 Neutrons-12 Electrons-10 *If the ion is positive, subtract e- *If the ion is negative, add e-

 Examples 7 3 Li O Mg 2+ Protons Neutrons-7-3=416-8=812 Electrons *If the ion is positive, subtract e- *If the ion is negative, add e-