Unit 3 Atomic Theory

Important terms to know Atoms – The fundamental unit of which elements are composed. Element – A substance that cannot be decomposed into simpler substances by chemical or physical means. It consists of the same type of atoms.

Abundances of Elements Nine elements account for about 98% of the earth’s crust, oceans and atmosphere.

Abundances of Elements The elements in living matter are very different from those in the earth’s crust. In the human body, oxygen, carbon, hydrogen and nitrogen are the most abundant elements.

Dalton’s Atomic Theory 1.All elements are composed of atoms. 2.All atoms of a given element are identical. 3.Atoms of different elements are different. 4.Compounds consist of the atoms of different elements. 5.Atoms are not created or destroyed in a chemical reaction.

Parts of an Atom Nucleus – The center of the atom, contains protons and neutrons. Electron cloud- the outer part of the atom where electrons are found. Nucleus Energy level

Part of the Atom Protons – located in the nucleus. Has a positive charge. Elements are unique to the number of protons it contains. Neutrons – located in the nucleus. Has a neutral charge. Electrons – located in the electron cloud. Has a negative charge.

Comparing parts of an atom

Anatomy of the Atom The Bohr’s Model of the atom suggests that the nucleus is in the center of the atom and the electrons are located outside the nucleus circling around in orbitals called energy levels.

The periodic table gives us clues to how many protons, neutrons, and electrons that a neutral atom contain. With this given information, you can easily build the structure of the particular atom

All you have to know the rules that atoms follows. Rules –The first energy level (or ring around the nucleus) only can hold 2 electrons –Once the first ring is “full”, the next set of electrons will begin to fill in to a new energy level. –With the exception of the first energy level, All outer energy levels only wants to have 8 electrons. This is called the Octet rule –Once the octet has been reached, a new energy levelwill be made.

How to draw an Atom As stated the Periodic table gives us clues on the structure of the atom.

How to draw an Atom Structure of Hydrogen –It has 1 electron –It has 1 proton –We will assume it has no neutrons

How will the Hydrogen look like? As you can see that there is 1 proton in the middle of the atom. There is only one energy level with 1 electron

Another example Structure of Lithium –Atomic Number 3 protons 3 electrons Lets assume that there is 4 neutrons. Lets draw it.

How does Lithium look like?

Try some examples Oxygen –Lets assume that It has 8 neutrons

Argon –Lets assume it Has 22 neutrons

Names and Symbols for the Elements Each element has a name and a symbol. –The symbol usually consists of the first one or two letters of the element’s name. –The first letter of the symbol is always in capital letters –Examples: Oxygen O Krypton Kr –Sometimes the symbol is taken from the element’s original Latin or Greek name. Examples: gold Au aurum lead Pb plumbum

Compound – a substance made of two or more different elements joined together in a specific way. Law of Constant Composition –A given compound always contains the same proportions by mass of the elements of which it is composed.

Formulas of Compounds A compound is represented by a chemical formula in which the number and kind of atoms present is shown by using the element symbols and subscripts. –Example: the simple sugar, glucose

Tools to Writing Formulas 1.Each atom present is represented by its element symbol. 2.The number of each type of atom is indicated by a subscript written to the right of the element symbol. 3.When only one atom of a given type is present, the subscript 1 is not written.

How to count Atoms If there is no numbers by the symbol of the element, assume only one –Na –MgO A subscript is a number written at the lower right corner of the chemical symbol. If there is more than one, then a number is used. –H2–H2 –Li 2 O

How to count Atoms A subscript outside a bracket multiples all the elements inside the bracket. –Mg 3 (PO 4 ) 2 A coefficient is a number written in front of a chemical symbol or in front of a chemical formula which indicates the number of atoms or molecules of the substance. –3 C –2 H 2 O

Lets Practice counting Atoms… 1.NaCO 3 2.Ca 3 (PO 4 ) 2 3.K 2 CrO BaCl 2 5.NH 4 C 2 H 3 O Al 2 (CO 3 ) 3 7.Pb(NO 3 ) (NH 4 ) 2 Cr 2 O 7

Chemical Symbols

Lets Practice…..

More Practice… ElementMass #Atomic ## of Protons # of Electrons # of Neutrons Be Na

More Practice…. ElementMass #Atomic ## of Protons # of Electrons # of Neutrons Be94445 Ne2010 Na P

What are Ions? Atoms can be either neutral or charged…. When they are neutral… # of protons = # of electrons When they are charged….. # of protons ≠ # of electrons These charged atoms are called Ions.

What are Ions? Atomic number (# of protons) Mass Number (# of protons + #neutrons) Charge

What are Ions? If charge is POSITIVE (+), that is how many more protons there are to electrons. If charge is NEGATIVE (-), that is how many more electrons there are to protons.

What are Ions?

More Practice… ElementMass #Atomic ## of Protons # of Electrons # of Neutrons F-F Se

More Practice… ElementMass #Atomic ## of Protons # of Electrons # of Neutrons F-F Ne Se P

Isotopes Isotopes are atoms with the same number of protons but different numbers of neutrons.

Diatomic Molecules

Average Atomic Mass Atomic Number Chemical Symbol Chemical Name Average Atomic Mass

Average Atomic Mass – the weighted average of the masses of all of the isotopes of an element.

Oxygen has 3 stable isotopes –O 16 –O 17 –O 18 It turns out in nature we see that of all oxygen… % is O % is O % is O 18

How is the average atomic mass is calculated? Remember Average Atomic Mass is a weighted average of all the isotopes of any particular element. There two things you need to know about each isotope in order to calculate the average atomic mass…. Mass and %Abundance

We know that there is 3 stable isotope of Oxygen: O 16, O 17, O 18 In order to calculate its average atomic mass, we need to know each isotope mass and %abundance. Atomic mass unit (amu) – a small unit of mass. 1 amu is equal to grams. Isotopes of Oxygen Mass (amu)%Abundance O O O

Isotopes of OxygenMass (amu)%Abundance O O O To calculate the average atomic mass: ( x )+(16.999x )+(17.999x ) = As you can see it turns out to be the same number on the periodic table. In the calculations be sure to change the percentage to decimal numbers. Make sure to move the decimal 2 times to the left.

Example The element copper has naturally occurring isotopes with mass numbers of 63 and 65.The relative abundance and atomic masses are 69.2% for a mass of 62.93amu for 63 Cu and 30.8% for a mass of 64.93amu for 65 Cu. Calculate the average atomic mass of copper. What do we need to know? Mass and %Abundance of each isotope 63 Cu 62.93amu 69.2% 65 Cu 64.93amu 30.8%

Example Lets calculate 63 Cu 62.93amu 69.2% 65 Cu 64.93amu 30.8% Make sure to change the percentages to decimal numbers (62.93x0.692)+(64.93x0.308) = Your answer should always match up with the element on the Periodic Table

Try this one Calculate the average atomic mass of sulfur if 95.00% of all sulfur atoms have a mass of amu, 0.76% has a mass of amu and 4.22% have a mass of amu. (31.972x0.95)+(32.971x0.0076)+(33.967x ) = Use the Periodic Table to check your answer.