Atomic Structure The smallest part of an element is an ATOM All atoms consist of subatomic particles: Protons Neutrons Electrons

Nucleus The “core” of the atom Contains 99.9% of the mass of the atom Protons and neutrons are found in the nucleus of an atom Mass Number = mass of the nucleus or mass of protons + neutrons

Protons Positively charged particles The number of protons identifies the element 1 proton = 1 atomic mass unit (amu) # protons = Atomic Number (whole number)

Neutron Neutral Particles Found in the nucleus 1 neutron = 1 amu # neutrons = Mass number – Atomic Number

Electrons Negatively charged particles Found in the electron cloud Electrons have a very small mass, so we don’t even count it! Electrons give atoms their chemical properties Atoms are neutral so; # electrons = # protons

Mass Number mass # = protons + neutrons always a whole number NOT on the Periodic Table! Neutron + Electrons Nucleus e- Proton e- e- Nucleus e- e- Carbon-12 Neutrons 6 Protons 6 Electrons 6 e-

Shorthand Notation Mass number SYMBOL OF ELEMENT Atomic number

C Isotopes Mass # Atomic # 12 6 Atoms of the same element with different mass numbers. Different number of neutrons & different mass 12 6 C Nuclear symbol: Mass # Each isotope has a different number of neutrons. Atomic # Hyphen notation: carbon-12; carbon-13 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Isotopes Neutron + Electrons Nucleus Nucleus Proton Proton Nucleus Carbon-12 Neutrons 6 Protons 6 Electrons 6 Electrons The chemistry of each element is determined by its number of protons and electrons. In a neutral atom, the number of electrons equals the number of protons. Symbols for elements are derived directly from the element’s name. Nuclei of atoms contain neutrons as well as protons. The number of neutrons is not fixed for most elements, unlike protons. Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes. Carbon-14 Neutrons 8 Protons 6 Electrons 6 Nucleus

6Li 7Li 3 p+ 3 n0 3 p+ 4 n0 2e– 1e– 2e– 1e– Nucleus Neutron Proton Electrons + Electrons + Nucleus Nucleus Lithium-6 Lithium-7 Neutrons 3 Protons 3 Electrons 3 Neutrons 4 Protons 3 Electrons 3

Cl Isotopes 37 17 Cl Chlorine-37 atomic #: mass #: # of protons: # of electrons: # of neutrons: 17 37 20 37 17 Cl Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Element symbol – Mass number Example Element symbol – Mass number Magnesium- 24 Magnesium-26 Mg-24 is atomic number 12 24 -12 = 12 n0 12=p+ 12 =e- Mg-26 is atomic number 12 26-12 = 14 n0 12=p+ 12 =e-

Atomic Mass Any sample of an element in nature is a mixture of isotopes of that element Atomic Mass – average mass of all the isotopes of that element as they occur in nature Atomic Mass is not a whole number since it is an average

Calculate the atomic mass of Cl. Atomic mass (chlorine) = (0.758)(35.0 amu) + (0.242)(37.0 amu) = 35.5 amu

Relative Atomic Mass 12C atom = 1.992 × 10-23 g atomic mass unit (amu) 1 amu = 1/12 the mass of a 12C atom Neutron + 1 p = 1.007276 amu 1 n = 1.008665 amu 1 e- = 0.0005486 amu Electrons Atomic mass 1. The mass of any given atom is not simply the sum of the masses of its electrons, protons, and neutrons. 2. Atoms are too small to measure individually and do not have a charge. 3. The arbitrary standard that has been established for describing atomic mass is the atomic mass unit (amu), defined as one-twelfth of the mass of one atom of 12C. 4. Most elements exist as mixtures of several stable isotopes. The weighted average is of the masses of the isotopes is called the atomic mass. 5. Electrons added or removed from an atom produce a charged particle called an ion, whose charge is indicated by a superscript after the symbol for the element. Nucleus Proton Nucleus Carbon-12 Neutrons 6 Protons 6 Electrons 6

Average Atomic Mass Avg. (mass)(%) + (mass)(%) Atomic Mass 100 weighted average of all isotopes on the Periodic Table round to 2 decimal places Avg. Atomic Mass (mass)(%) + (mass)(%) = 100 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Calculating Average Atomic Mass You will be given the mass number and the Percent Abundance (how common the isotope is in nature) of the isotope Atomic mass = (% abundance in decimal form isotope1)(mass isotope1) + (%abundance in decimal form isotope2)(mass isotope2)

Cl 35.4594 17 100 Mass spectrum of chlorine. Elemental chlorine (Cl2) contains only two isotopes: 34.97 amu (75.53%) and 36.97 (24.47%) 90 80 Cl-35 70 AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447) 60 AAM = (26.412841 amu) + (9.046559 amu) AAM = 35.4594 amu 50 Abundance 40 30 Cl-37 Mass spectrum of chlorine. Elemental chlorine (Cl2) contains only two isotopes: 34.97 amu (75.53%) and 36.97 (24.47%) 20 10 34 35 36 37 Mass

Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. Atomic Mass (16)(99.76) + (17)(0.04) + (18)(0.20) 16.00 amu = = 100 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Average Atomic Mass (35)(8) + (37)(2) 10 Avg. Atomic = = Mass EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. Avg. Atomic Mass (35)(8) + (37)(2) = = 35.40 amu 10 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Example Carbon has 6 protons and 6 neutrons, what is Carbon’s mass number? C-12 An isotope of Carbon has 6 protons and 8 neutrons, what is carbon’s mass number? C-14 Remember the number of protons NEVER changes for an element!

Isotope Review Same element different number of NEUTRONS Different Mass number Same Atomic number, therefore the same number of protons and electrons

Isotope Applications Complete the read around the room station activity

Atomic Structure ATOMS IONS ISOTOPES Differ by number of protons Differ by number of electrons ISOTOPES Differ by number of neutrons

Electrons Electrons give elements their chemical properties The arrangement of the electrons will determine how it reacts with other substances Gain electron the atom becomes negative (anion) Lose an electron the atom becomes positive (cation)

Humor Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure??” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of sodas. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

Electrons are found in the electron cloud The cloud has regions of space called energy levels The first energy level holds 2 electrons The second energy level holds 8 electrons. The third energy level holds 18 electrons

Valence Electrons Are found furthest from the nucleus Dictate the physical and chemical properties of an element Use the periodic table to determine the number of valence electrons. All atoms want 8 valence electrons

Lewis Dot Diagram A way to illustrate the number of valence electrons Use one dot for each valence electron Place the dot around each side of the symbol before pairing the electrons The symbol represents the nucleus plus all the inner electrons for the element.

Examples H O N F Ne

Electrons and Light Electrons are normally in the ground state When the atom is given energy the electrons move to the excited state. When the electrons lose this energy they fall back to the ground state and emit light. Each element has a unique emission spectrum

Electromagnetic Spectrum Electromagnetic Radiation – A broad range of energetic emissions made up of photons Photons – bundles of energy Travel like waves Move at the speed of light = 3.0 x 108 m/s Electromagnetic waves do not require a medium to move

Parts of the wave Amplitude – the height of the wave Wavelength – the distance between the two successive waves Frequency – the number of waves that pass a given reference point per second

Wavelength = lamda unit is nanometer Frequency = nu in units of 1/s or s-1

What is the difference between these waves?