Chapter 20 Section1: Stability in Bonding Chemical Bonds Chapter 20 Section1: Stability in Bonding

Combined Elements What do pennies and the Statue of Liberty have in common?

Both the Statue of Liberty and Pennies are coated in COPPER. Combined Elements Both the Statue of Liberty and Pennies are coated in COPPER. What is different about the coating Statue of Liberty that makes it that distinct green color?

Combined Elements CuSO4 Cu What elements are in Copper Sulfate?

New Properties When elements combine, the properties of the new COMPOUND can be very different than the elements alone.

Formulas A chemical formula tells what elements a compound contains and the EXACT number of atoms of each element in that compound. (i.e. H20, NaCl, H2SO4) - The number found in between elements is known as the SUBSCRIPT. This number tells you how many of a particular element you have.

Formulas The number found in between elements is known as the SUBSCRIPT. This number tells you how many of a particular element you have. C2H6O - No subscript means there is only “1” atom of that particular element

Formulas So what does a chemical formula tell you? C11H17N3O8 Tetrodotoxin

Atomic Stability Why do elements form compounds to begin with? - Before we answer, we need to learn about lewis dot structures…

How to make Lewis Dot Structures Start with the Symbol of an element (Pick any main group element to try) C

2. Determine the group number of that element 2. Determine the group number of that element. (Numbers will be between 1-8) Carbon is in group 4 C

3. Going clockwise and starting at the the top of the element, place a dot at each side of the symbol. C The number of dots you use = the group number That’s it. Now do the first 10 elements.

Chemical Stability What did you notice about those elements in group 8? What was special about these elements? All elements want an outer shell just like the noble gases.

How do the elements get a stable outer shell? Atoms with a partially stable outer shell can gain, lose, or share electrons until they are stable.

Chemical Bonds When atoms gain, lose, or share electrons, an attraction forms between two atoms, pulling them together to form a compound. This is known as a chemical bond.

Types of Bonds When an atom gains or loses electrons, it forms an ION: a charged particle with more or fewer electrons than protons. If an ion has more electrons than protons, what charge will it have, positive or negative?

IONIC BONDS When an atom loses or gives away an electron, the ion gets a +1 charge. When an atom gains an electron, the ion gets a -1 charge. This can be written as a superscript (written above).

Ionic Bonds When the electron is TRANSFERRED, an attraction occurs between the two ions. This forms an IONIC BOND.

Covalent Bonds Some nonmetals are unlikely to gain or lose electrons. For example carbon, in group 4. Is it easier for carbon to give away 4 electrons, or take 4 in?

Covalent Bonds Atoms like this become stable from SHARING electrons with other atoms. This is called a COVALENT BOND. When these atoms combine, they form a MOLECULE. In the above model, two shared dots equal 1 bond.

Multiple bonds Covalent bonds can form more than one bond between two atoms. Why?

POLAR BONDS Sometimes when you have covalent bonds, there is not an equal sharing of electrons. If an ion has a stronger pull on the shared electrons, it will have a PARTIAL NEGATIVE charge. If an ion has a weaker pull, it has a PARTIAL Positive charge.