Atomic Structure

What is an atom? Atom: the smallest unit of matter that retains the identity of the substance First proposed by Democratus

Atomic Structure Atoms are composed of 2 regions: Nucleus: the center of the atom Accounts for the atomic mass of the atom Electron cloud: surrounds the nucleus Accounts for majority of the space in an atom Nucleus Electron Cloud

Subatomic Particles The atom is composed of 3 subatomic particles: 1) Protons (positive) p+ 2) Electrons (negative) e- 3) Neutrons (neutral) n

What’s in the Nucleus? Both protons and neutrons are found in the nucleus Neutrons Protons

What’s in the Electron Cloud? Electrons are found orbiting the nucleus in the electron energy shells (n) Electrons

How is the overall change of an atom zero (neutral)? This is because the # of protons = the # of electrons Protons = Electrons Example: Protons = +20 Electrons = -20 Overall charge = 0

How do we know the number of subatomic particles in an atom? Atomic number = number of protons Ex: Hydrogen’s atomic number is 1 So hydrogen has 1 proton Ex: Carbon’s atomic number is 6 So carbon has 6 protons **The number of protons identifies the atom. Example: 2 protons = Helium (He) 29 protons = Copper (Cu)

Learning Check #1 Identify the element using the number of protons given A) Protons = 20 Calcium (Ca) B) Protons = 56 Barium (Ba) C) Protons = 53 Iodine (I)

How do we know the number of subatomic particles in an atom? Mass number: protons + neutrons found in the nucleus of an atom Mass # - Atomic # = # of neutrons Example: Sodium (Na) Mass # = 23 Protons = 11 23 -11 = 12 neutrons

Learning Check #2 Find the number of neutrons in the following using the Mass # equation A) Lithium (Li) 3 3 Atomic #= _______ = _______protons 7 Mass # = _______ 4 7 – 3 = 4 neutrons # Neutrons = ______ B) Neon (Ne) 10 10 Atomic # = ______ = ______ protons Mass # = ________ 20 20 – 10 = 10 neutrons # Neutrons = ______ 10

What about the electrons? The electrons are equal the protons atomic # = protons = electrons Example: Helium (He) atomic # = 2 mass # = 4 p+ = 2 4 – 2 = 2 neutrons e- = 2 n = 2

Learning Check #3 Determine the number of subatomic particles in the following: A) Chlorine (Cl) Atomic # = ____ 17 Mass # = _____ 35 p+ = ____ 35 – 17 = 18 neutrons e- = ____ n = ____ 18 B) Potassium (K) Atomic # = _____ 19 Mass # = _____ 39 p+ = ____ 39 – 19 = 20 neutrons e- = ____ n = ____ 20

Bohr Model of the Atom Example: Neon (Ne) Atomic # = 10 Mass # = 20 20 – 10 = 10 neutrons Atomic # = 10 Mass # = 20 Nucleus = all protons and neutrons n3 = 18 e- n1 = 2 e- n4 = 32 e- n2 = 8 e- 10 10 10 p+ = _____ e- = _____ n = _____

n1 is full. Must put the remaining 4 electrons in n2 Learning Check #4 Place the electrons in the correct energy shells on the Bohr Model below for Carbon (C) Find number of protons, electrons and neutrons first mass # = __ atomic # = ___ 6 12 2 e- in n1 6 p+ and 6 n in the nucleus n1 is full. Must put the remaining 4 electrons in n2 4 e- in n2 12 – 6 = 6 neutrons p+ = ___ 6 e- = ___ 6 n = __

Mass # Atomic # Symbols Hyphen notation: carbon - 12 (mass #) Show the Symbol of the element, Atomic number, & Mass number Mass # Atomic # Hyphen notation: carbon - 12 (mass #)

Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of Chlorine 35 Cl 37 Cl 17 17 Chlorine - 35 Chlorine - 37

Isotopes Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons. Neon-20, neon-21, and neon-22 are three isotopes of neon, a gaseous element used in lighted signs. Comparing and Contrasting How are these isotopes different? How are they similar?

Isotopes Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 2

Average Atomic Mass To calculate the average atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

Atomic Mass + Atomic Mass = + ….. (Mass isotope # 1) (% Abundance)

Rubidium has two common isotopes, 85Rb and 87Rb Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?