Subatomic Particles In an atom Protons and neutrons are clumped together in a very small dense nucleus The Electrons are found outside of the nucleus in.

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Presentation transcript:

Subatomic Particles In an atom Protons and neutrons are clumped together in a very small dense nucleus The Electrons are found outside of the nucleus in the electron cloud

It is NOT that simple Within the electron cloud there are different principal energy levels (more to come)

Principle Energy Levels Principle Energy Levels are found at different distance from the nucleus Lowest energy levels are closest to the nucleus Highest energy levels are farthest from the nucleus

Remember the periods… Elements in the same row of the periodic table have the same number of occupied energy levels

H and He, have one energy level Li thru Ne, have two energy levels AND so on…

Bohr The Bohr model is used to show electron placements in the energy levels.

Steps to drawing a Bohr model First step: Determine the number of protons, neutrons and electrons in each element. Second step: Represent the nucleus as the chemical symbol and indicate the number of protons and neutrons. Third step: Making larger circles around to represent # of energy level

Steps to drawing a Bohr model Fourth step: Place electrons into the different energy levels (closest first) following the maximum # of electrons and the octet rule

Determine # of Electrons in each energy level (part 1) The electrons in an atom will fill the lower energy levels before filling the higher energy levels Electron Capacity = 2n2 n = the quantum #, the same as the energy level in question

Energy Levels First energy level- max 2 electrons Second energy level- max 8 electrons Third energy level- max 18 electrons Fourth energy level- max 32 electrons

BUT WAIT IT IS NOT THAT EASY!

Octet Rule Even though an energy level can contain more electrons, it stops adding at 8 electrons because having 8 electrons in an energy level makes it stable This is why Noble Gases don’t react

Exceptions to the rule Exception – 1st energy level will be stable at max # of 2 electrons This only works easily for the 1st 20 elements

Why is this important Because the valence electrons determine the how the atom reacts and forms bonds What are valence electrons?

Valence Electrons The electrons that occupy the highest energy level (outtermost) Determines atoms likelihood of being involved in chemical reactions Stable – non-reactive Unstable - reactive the number of valence electrons determines an element’s chemical properties

Look Back at Bohr Models Moving across a period, what happened to the number of valence electrons. Compare Bohr Model of Li and Na What Trends do you notice?

Valence Electrons elements in the same column of the Periodic Table have the same number of valence electrons and have similar chemical properties.

Valence Electron Patterns ~SKIP~

Stable Atoms Have 8 valence electrons (2 valence electrons if only 1st energy level is present) Non-reactive

UNstable atoms Do NOT have 8 valence electrons (or 2 if only 1st energy level is present) These atoms react with other atoms to achieve stability HOW?

It’s all about electrons! Atoms will gain, lose, or share electrons to become stable and will form chemical bonds

Molecules A molecule is neutral chemically bonded group of atoms that act as a unit. Molecules consist of two or more atoms. (not 2 or more elements)

Molecules Diatomic molecules consist of two of the same atom. Ex. O2, N2, F2, Cl2, Br2, I2, H2

Compounds Compounds are formed when two or more different elements combine. All compounds are molecules but not all molecules are compounds.

What does that mean? Ex = H2O is a compound & molecule Ex = Br2 is molecule NOT a compound

Compounds Two types -covalent (also called molecular) compounds -ionic compounds

Covalent Compounds Made of two or more nonmetals. Formed when electrons are shared between the atoms This is a covalent bond Smallest particle is called a molecule.

Covalent Compounds Properties include: Low melting and boiling points Tendency to be soft and flexible

Covalent Compounds Do not conduct electricity There are no electrons available to carry the current. When in water, these compounds dissolve as molecules not ions.

Covalent Compounds These compounds will dissolve in other covalent compounds.

Ionic Compounds Form as the result of the attraction between of positive and negative ions

Ionic Compound Example Na - Based on #p and #e; (11 p + 10 e- = +1) Na positive ion Fl – Based on #p and #e; (9 p + 10 e- = -1) Fl negative ion ionic bond results from the attraction of opposite charges. sodium fluoride

Ion Review Ion – atom or groups of atoms with an overall charge. Charge can be positive or negative. Ions are formed when electrons are lost or gained.

Ions If electrons are lost, a positive ion is formed = CATION If electrons are gained, a negative ion is formed = ANION

Ionic Compounds The number of electrons gained or lost is shown along with the symbol of the element. A + following the number indicates a positive charge. A – indicates a negative charge.

Ionic Compounds Properties of ionic compounds include: High melting and boiling points Tendency to be hard and can be split.

Ionic Compounds Most conduct electricity when dissolved in water or when molten. The ion separate in water. This allows for the conduction of electricity.

Ionic Compounds Ionic solids do not conduct electricity. (must be dissolved or molten) The ions do not separate. As solids, ionic compounds are good insulators. Many are soluble in water.

Ion Charges The number of electrons that it has lost or gained determines an ion’s charge Ions that GAIN electrons have a NEGATIVE charge and are called anions. Ions that LOSE electrons have a POSITIVE Charge and are called cations.

Atoms losing and Atoms gaining In our last example; the Na lost an electron – where did it go? F gained that electron

We can figure out the number of electrons either being lost or gained without being told

Electrons are Lazy! In order to be a stable atom the outside shell must either be completely filled with electrons or emptied (leaving the next shell filled). To do this, you must decide if it’s easier to lose or gain electrons.

Column # # Valence Bohr Model # Gain to be 8 # Lose to be 0 Gain or Lose ? Charge?

Lithium Loses an Electron Li  Li+1 + 1 e-

Fluorine gains an electron F + 1 e-  F-1

Ionic Bond = LiF

What if it was Mg instead of Li Bohr Model of Each Mg and F How many electrons does Mg need to gain or lose? How many can F gain or lose? What is the problem? What is the solution?

Ionic Bond = MgF2

Review Based on number of valence electrons, we can determine whether atoms will gain or lose electrons, and then we can determine the number of atoms of each element needs to make all atoms involved STABLE Provides chemical formula

Remember covalent is a little different Two non-metals***** Electrons are shared not lost and gained

Covalent Examples C H H is going to share its 1 electron with C; this electron counts for both H and C H is stable it has 2 electrons in 1st energy level Carbon now has 5 electrons, what needs to happen? C H

Covalent Example (cont.) Covalent Bonds Compound = CH4

Okay… Lets make it a little easier Only valence electrons involved in bonding Use Lewis Dot Structures

Lewis Dot Diagram show the bonding between atoms of a molecule by using the valence electrons.

Energy Level ‘Clouds’ hoku.as.utexas.edu/.../a309f04/lect1cos.html phycomp.technion.ac.il/~phr76ja/lecture1.html