Atomic Structure Take notes on the appropriate page in your packet

Atoms -The Building Blocks of Matter

Atoms Smallest possible unit into which matter can be divided, while still maintaining its properties. Made up of: protons neutrons electrons

Atoms are so small that… it would take a stack of about 50,000 aluminum atoms to equal the thickness of a sheet of aluminum foil from your kitchen. a human hair is about 1 million carbon atoms wide. a typical human cell contains roughly 1 trillion atoms. a speck of dust might contain 3x10 12 (3 trillion) atoms. C-C-C-C-C-… + 999,995 more 1 trillion atoms .

Protons (+) Positively charged particles Located in the NUCLEUS Identify the atom Never change

Protons = Atomic Number = # of electrons = 1 atomic mass unit (amu) Atomic Number = Number of Protons

Atomic Number The number of protons in the nucleus of an atom What would be the atomic number of this atom?

Neutrons Neutral particles; have no electric charge Located in the NUCLEUS of the atom = 1 atomic mass unit (amu)

Electrons (-) Negatively charged particles Found outside the nucleus of the atom, in the electron shells Mass is insignificant when compared to protons and neutrons = # of protons in a neutral atoms Involved in the formation of chemical bonds

The Atom’s “Center” Protons and neutrons are grouped together to form the “center” or nucleus of an atom Notice that the electrons are not apart of the nucleus - -

Mass Number The total number of PROTONS + NEUTRONS in an atom’s nucleus Expressed in Atomic Mass Units (amu) Each proton or neutron has a mass of 1 amu Average Atomic Mass

Mass Number  3 3  4 4 What would be the mass number of this atom? 3 protons + 4 neutrons = a mass number of 7 amu Why did we not account for the electrons when calculating the mass number?

Hydrogen (H) Atom Notice the one electron in the first orbital + - Even though there are no neutrons present, Hydrogen is still considered an atom + - = 1 = 0 = 1 What’s the atomic number of this atom? What’s the mass number of this atom? 1 1

Oxygen (O) Atom Notice the two electrons in the first orbital/level and the six in the second = 8 What’s the atomic number of this atom? What’s the mass number of this atom? 8 16

Sodium (Na) Atom Notice the two electrons in the first orbital/level, eight in the second, and one in the third = 11 = 12 = 11 What’s the atomic number of this atom? What’s the mass number of this atom? 11 23

Short hand form AZ Notation Ex. A Z X A = mass number Z = atomic number X = Element Symbol So… 12 6 C shows that Carbon has an atomic number of 6 (6 protons) and a mass number of 12 (6 protons and 6 neutrons) 14 7 N: How many protons? ____ Electrons? ____ Neutrons?__ S: Protons? _____ Electrons? ______ Neutrons? ____ Cl: Protons? ______ Electrons? _________ Neutrons? _____

Isotopes All atoms of the same element have the same number of protons; however, atoms of the same element with different numbers of neutrons are called isotopes Hydrogen (Protium)Hydrogen (Deuterium)Hydrogen (Tritium) Notice that each of these atoms have one proton; therefore they are all types of hydrogen. They just have a different mass number (# of neutrons).

Isotopic Notation… For example, all carbon atoms have 6 protons (definition of carbon.) Most carbon atoms have 6 neutrons (mass number of 12.) Carbon – 12 OR C – 12 But some carbon atoms have 8 neutrons, giving them an mass number of 14. Carbon – 14 OR C-14 Element Name – mass number OR Element Symbol – mass number

Calculating Atomic Mass The “atomic mass” is similar to the mass number; it is the decimal number found in the periodic table. The atomic mass is the weighted average of the masses of all the naturally occurring isotopes of an element The average considers the percent abundance of each isotope in nature Take the percent and convert it into a decimal Multiple the decimal by its coordinating mass number Add the numbers together Ne(20)90.60 Ne(21)0.26 Ne(22)9.20 Let’s Practice! Calculate the average atomic mass of Neon. Below you will find 3 isotopes of Neon and each’s percent abundance. Atomic Mass of Ne * * *22 = =

Calculating Atomic Mass Hydrogen (Protium) Mass # = 1 amu Hydrogen (Deuterium) Mass # = 2 amu Hydrogen (Tritium) Mass # = 3 amu What would be the atomic mass (≈) of Hydrogen if these three isotopes were found in the following percentages (99.9%, 0.015%, 0%) respectively?

Calculating Average Atomic Mass Ex. An element has 3 isotopes: 24.1% of all the isotopes have a mass of amu, 48.7% have a mass of 74.61, and 27.2% have a mass of What is the average atomic mass of the element? Convert percent to a decimal by moving the decimal 2 places to the left. Multiple each % by its mass Add together The sum is the average atomic mass.

How to determine most abundant isotope Calcium has 3 isotopes. One has a mass of 35amu, another 41amu, and another 40amu. Which isotope is the most abundant? Look at the atomic mass to determine most abundant isotope!