Introductory Chemistry Mrs. Taktak and Mrs. Storey

Atoms Most of 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?

Isotopes Most atoms have different forms due to differing #’s of neutrons. These different forms of a particular atom are known as isotopes of that atom. Why can the neutron # be different without affecting the atom?

Isotope Practice There are two forms of carbon: Carbon-12 (C-12) and Carbon-14 (C-14) Show the proton, electron, and neutron #’s for each isotope of carbon: Carbon-12:Carbon-14: p + =p + = e - =e - = n 0 =n 0 =

Do Atoms Ever Combine? Yes! They form compounds. Define a compound: Why do elements combine to form compounds? It has to do with the # of electrons in the outer shell of the atoms. All electrons in the outermost shell are called Valence Electrons

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?

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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! There are structural formulas which are the atomic drawings for molecules, such as what you drew for water.

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

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!

Are there other kinds of bonds? Yes! There are also Ionic Bonds. Ionic Bonds are formed by an attraction of positive and negative charges. Where do the charges come from if the atoms are neutral????

Example of an Ionic Bond Draw the atoms Na and Cl. Notice that Na has 11protons and 11 electrons. This gives Na 1 electron in its outer shell. Is Na happy this way? Is it likely to share to make 8? Notice that Cl has17 protons and 17 electrons. This gives Cl 7 electrons in the outer shell. Is Cl happy?

A solution! If Na could lose an electron, and Cl could gain an electron, they would both be “happy.” This is how Ionic Bonds are formed. An Ionic Bond is formed when electrons are transferred from one atom to another, which results in opposite charges that attract each other.

emistry.com/links/ bonding/bondingfl ashes/bond_types.swfwww.kentch emistry.com/links/ bonding/bondingfl ashes/bond_types.swf

How are the charges formed? When Na loses its electron, how many electrons does it have now? How many protons does it have? This gives Na a (+) charge, making it a + ion (cation). Understanding this, explain how Cl becomes (-) charged when it takes on Na’s electron, making it a – ion (anion). +/- attract, and a molecule of NaCl is formed, which is the molecular formula for table salt!

More on Ionic Bonding When these atoms lose or gain electrons, they get “new names”. Na is now called Na+ or a (Sodium Ion) Cl is now called Cl- or a (chloride ion) Any positive ion is called a Cation Any negative ion is called an Anion

Practice Problems (select 2, get checked when finished with 1) MgOCaBr 2 LiFBe 3 P 2 PbBr 4 Be 3 N 2 Li I K 2 O