Introductory Chemistry Mrs. Taktak and Mrs. Storey

Atoms The Universe consists of matter and energy.matter All matter is composed of basic elements. All elements are composed of Atoms. What is an atom??? –The smallest unit of matter that has all the properties of a given element. Ex.: Gold is made up of only gold atoms!

What does an Atom look like? In the center is a Nucleus In the nucleus are 2 smaller particles called: Protons and Neutrons –Protons have a (+) charge and Neutrons have (0) charge. Each element has a different number of protons in the nucleus. It is this proton # that gives the atom (element) its characteristics.

What does an Atom look like? Outside the nucleus are rings called shells. Floating around in the shells are Electrons. Each shell holds a specific # of electrons. (We will talk more about this later.) What charge do you think an electron has?

Time Out!! Label this atom

Here are some pictures of Atoms

Drawing Atoms To draw an atom correctly, you need to use the Periodic Table of Elements.

How to Use the Table for Drawing Atoms Atomic # = # Protons = # Electrons Why does the proton # = the electron #?

Let’s practice!! The 1 st Element on the Periodic Table is Hydrogen. It has an Atomic # of 1, so it has ___ Proton and ___ Electron. Nucleus with 1 proton 1 st shell 1 Electron

You Practice! Using your periodic table, can you guess which element this is?

Drawing larger atoms After Hydrogen and Helium, we have to add another shell to put electrons on. Why? Because: The 1 st shell only holds 2 electrons. All other shells want to hold 8 electrons. Practice drawing Lithium, Beryllium, Boron, and Carbon.

How do we find # of Neutrons? We know that the Atomic # = # Protons and # Electrons, but how do we find # of Neutrons? It’s easy! Take the Atomic Mass # and subtract the Atomic #. (A.M.- A. # = # of Neutrons) What is the # of Neutrons for Carbon?

Practice Using your above examples (Lithium, Beryllium, Boron, Carbon), calculate the number of neutrons for each and label on your diagrams.

Another way to Represent Atoms We can use Lewis Electron Dot models to represent atoms. Why? So we can more easily see how atoms will combine to form compounds. (Next lesson).

Lewis Electron Dot models 1 st - Write down the Chemical Symbol 2 nd - Find out what column the element is in on the periodic table (might need to renumber your periodic table) 3 rd - Put the appropriate number of electrons (as dots) around the chemical symbol.

Example: This is P for Phosphorus. It has an atomic number of 15. So it has 15 electrons. We only record the electrons in the outer most shell. To find out how many that is, we can look at the column it is in. Which is????? All electrons in the outermost shell are called Valence Electrons

Practice For each of the elements listed below, write the chemical symbol and the number of valence electrons around each. 1. Lithium 2. Oxygen 3. Chlorine

Do Atoms Ever Combine? Yes! They form compounds. Define a compound: Two or more atoms joined together. Why do elements combine to form compounds? It has to do with the # of electrons in the outer shell of the atoms (valence electrons).

Types of Bonds There are many types of bonds. Examples include: Covalent, Ionic, Metallic, Hydrogen… In Biology class, we are most interested in studying the Covalent Bond because this type of bond is what makes up the majority of compounds in living things.

Bonding There are 2 “rules” that you need to know about atoms. 1. The first shell wants to hold 2 electrons 2. The 2 nd, 3 rd,..shells want to hold 8 electrons

Is this a happy atom?

Covalent Bonding This occurs when atoms share electrons to become stable, or “happy”! The shared pair of electrons provides each hydrogen atom with two electrons in its valence shell

More Examples A molecule of water is formed by a covalent bond. Oxygen has 6 electrons on its outer shell, so it wants _____ more? Hydrogen has 1 on its outer shell, it would like to have ____ more? Can you guess how this bond is drawn?

g/bondingflashes/bond_types.swf

More On Covalent Bonds Covalent bonds are very strong bonds. It is hard to break a covalent bond. Example, your hair is held together by covalent bonds. It takes energy to break these bonds, and a strand of your hair!

How do we write the formulas for these molecules? There are chemical formulas, which are the written chemical symbols and their subscripts. Example: Water is written as H 2 O. This is the chemical formula for water!

Practice For the compounds given below, tell how many of each atom there are. 1.CO 2 = ______ Carbon and ____ Oxygen 2.CH 4 = ______ Carbon and ____ Hydrogen 3.H 2 O 2 = _____ Hydrogen and ___Oxygen

Practice (Covalent)! Try drawing a molecule of Oxygen gas which is O 2. OR Try drawing a molecule of methane, which is CH 4.