Chemical Bonds and Compounds

Chemical Bonds and Compounds Section 1: Elements Combine to Form Compounds

Compounds A compound contains two or more different elements that are chemically bonded together.

Mixtures A mixture contains two or more elements and/or compounds that are not chemically bonded together.

Chemical Bonds How do atoms form chemical bonds with other atoms? They share valence electrons with each other so that they have full outer shells. Example: Water - H2O

Molecules and covalent bonds A chemical bond forms when atoms transfer or share electrons. A covalent bond is formed when atoms share electrons.

Bonds Single Bond – share 2 electron Double Bond – share 4 electrons Triple Bond – share 6 electrons Single bond C C C2 carbon-carbon

Chemical formulas and diagrams Molecules are represented by a chemical formula. The chemical formula tells you the precise number of each kind of atom in the molecule.

Chemical Formulas Elements want a full outer shell. So elements give or take electrons so that their shell is full. The sum of the charge of their ions must equal zero. Ex: NaCl MgO MgCl2 Na+ Cl- Mg2+ O2- Mg2+ Cl- Cl- (+1) + (-1) = 0 (+2) + (-2) = 0 (+2) + (-1) + (-1) = 0

Ionic bonds Ionic bonds are bonds in which electrons are transferred from one atom to another. Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.

Same Element, Different Compounds The same elements can make up compounds that are very different Examples: Water (H2O) Hydrogen Peroxide (H2O2)

Questions Write these questions as an output. Leave space after each question. Answer the questions in that space. How do the properties of compounds often compare with the properties of the elements that make them up? How many atoms are in the compound C12H22O11? How can millions of compounds be made from the atoms of about 100 elements? If a chemical formula has no subscripts, what can you conclude about the ration of the atoms in it? How might you distinguish between hydrogen peroxide and water? A chemist analyzes two compounds and finds that they both contain only carbon and oxygen. The two compounds, however have different properties, How can two compounds made the same elements be different? What part of an atom is involved in chemical bonding?