Chapter 7 Atoms and Bonding

Can you fill in the blank? The Atom The nucleus has a ________ charge. Located outside of the nucleus are electrons with a ________ charge. The negative charge of the electrons are __________ by the positive charges from the protons. The atom as a whole is _________. Explain what that means for the electrons and protons? _________________________________________

Electron Cloud and Energy Levels There are electron energy levels in the electron cloud outside the nucleus. Each energy level has a certain electron capacity. 1st Energy Level (Innermost) : electron capacity of 2 2nd Energy level: electron capacity of 8 3rd Energy level: electron capacity of 18 4th Energy level: electron capacity of 32 5th Energy level: electron capacity of 32

Electron Energy Levels

What is important about the electrons in the Outermost Energy Level? The electrons in the outermost energy level are called the Valence Electrons. The valence electrons determine how atoms form bonds with other atoms. The valence electrons determines the Family the element belongs to on the Periodic Table. The Family of the Periodic table are the columns. (See illustration) The valence electrons determines the physical properties of the element.

The Valence Electrons are colored in black in the diagrams below . . . . .

Let’s Practice Find the valence electron number for atoms: Helium ____ Aluminum ____ Polonium ____ Chlorine ____ Potassium ____ Argon ____

Lewis Electron Dot Diagrams Is used to represent the available valence electrons in the outer shell of an atom. Valence electrons are represented by dots around the chemical symbol. Steps in Drawing the Lewis Dot Diagram: Write the symbol of the element. Identify the valence electrons for the element. Ex: Ne has 8 valence electrons Start placing your dots to represent each valence electron.: TOP BOTTOM LEFT RIGHT DOUBLE UP. ** You can place a max. 2 dots on each side equaling 8 dots total. ** Hydrogen and helium, are exceptions, you can place 2 dots on one side of the symbol.

Examples

Practice with Lewis Dot Diagrams Hydrogen Selenium Lithium Magnesium Nitrogen Arsenic Bromine Barium

Watch the video: https://www.youtube.com/watch?v=900dXBWgx3Y Answer the following: How can you form an ion? What are positively charged atoms called? What are negatively charged atoms called?

So why do atoms like to find a friend? “You complete me!!” Atoms want to complete their outer shell of electrons, that is why they make friends. This is a bond. The combing of atoms of electrons to make a new substance is called a chemical bond. Forming a bond is determined by their structure, and valence electrons. There are two types of bonds we will learn: Ionic Bonding Covalent Bonding

Ionic Bonding Ionic Bonding is the transfer of electrons from one atom to another: one atom will lose an electron and the other atom will gain the electron. So they can complete their outer shell to 8 electrons! https://www.youtube.com/watch?v=zpaHPXVR8WU

Rules When Forming Ions: If an atom loses an electron, it becomes more positive forming a positive ion called a Cation If an atom then gains an electron, it becomes more negative forming a negative ion called an Anion. https://www.youtube.com/watch?v=900dXBWgx3Y

So, what does that mean for each atom So, what does that mean for each atom? What do you think will happen to their neutral charge if they gain or lose an electron? Ionic bonding will create ions. What is an Ion? Ions: are atoms with a charge of either positive (+) or negative (-). https://www.youtube.com/watch?v=900dXBWgx3Y

Example of Ionic Bonding Cation Anion Forming Sodium chloride

What is needed for an Ionic Bond to form? What is required for any action or reaction to take place in science? ENERGY! Known as Ionization Energy. Which action will require more energy? Think! Atoms that can lose a small amount of valence electrons have a low ionization level? Atoms that have a large amount of valence electrons have a high ionization level? These are the Anions which have a strong attraction for electrons known as the electron affinity.

Ionic Compounds form a Crystal Lattice A crystal lattice is composed of many ionic bonds. A crystal lattice creates great stability It has important physical properties: Very high melting points, Ex. NaCl (Sodium Chloride) Crystal solid

Covalent Bonding A bond between two non metals! Some cases atoms have very high ionization energies and very high electron affinity. Therefore, atoms must then share their electrons, known as Covalent Bonding! https://www.youtube.com/watch?v=KjoQHqgzda8 https://www.youtube.com/watch?v=MklJpbJVDe4

Ionic versus Covalent Bonding https://www.youtube.com/watch?v=PKA4CZwbZWU Ionic versus Covalent Bonding Ionic bonds take place between ______ and ______. Covalent bonds take place between ______ and ______. Ionic bonds create _________. Covalent bonds create__________ bonds. Ionic bonds take place when atom _______ an _________ and another atom _________ _________. Covalent bonds take place when ___________ are __________ between atoms.

Expressing covalent bonding Covalent bonding can occur between the same elements, known as: Diatomic Bonds. Ex: Cl2 or H2 Cl Cl H H

How Do We Draw a Lewis Dot Diagram for Covalent Bonding? Write the Symbol for each element about 2 cm apart. Identify the valence number for each element. Figure out how many valence electrons each element needs to complete the Octet Rule Place that number of dots in the middle of the two symbols. Then draw in the remaining valence dots for the first atom in their appropriate location. Do the same for the joining atom Suggestion: use X to represent the other element’s valence electrons. F2 F F

Let Us Try it Again H2O H O H

H O H What is a molecule? The covalent bonding of two or more atoms!! Ex: H2O H O H