Atoms and Bonding Chapter 10-1

We learned that atoms have a nucleus and an electron cloud. The nucleus contains the protons and the neutrons (p+, n neutral). The electron cloud contains the electrons (e-)

The different areas for an electron in an atom are called energy levels. The energy level corresponds to the period in which the element is found. Electron Arrangement— Electron Energy Why do atoms combine? This shows a model of what these energy levels might look like. Each level represents a different amount of energy.

Period number = Energy Level

The farther an energy level is from the nucleus, the more electrons it can hold. Number of Electrons Why do atoms combine? The first energy level, energy level 1, can hold one or 2 electrons, the second, energy level 2, can hold up to 8, the third can hold up to 18, and the fourth energy level can hold a maximum of 32 electrons. Use this equation 2n 2 to find the number of electrons that an energy level can hold, where n equals the period number.

The stairway, shown here, is a model that shows the maximum number of electrons each energy level can hold in the electron cloud. Energy Steps Why do atoms combine? Use this equation 2n 2 to find the number of electrons that an energy level can hold, where n equals the period number.

Electrons in the level closest to the nucleus have the lowest amount of energy and are said to be in energy level one. Electrons farthest from the nucleus have the highest amount of energy and are the easiest to remove. The closer a negatively charged electron is to the positively charged nucleus, the more strongly it is attracted to the nucleus. Therefore, removing electrons that are close to the nucleus takes more energy than removing those that are farther away from the nucleus. Energy Steps Why do atoms combine?

Octet Rule for Valence electrons The energy levels have sub-levels called shells and the electrons are placed in these shells according to rules. The 1st shell can hold up to 2 electrons, and each shell thereafter can hold up to 8 electrons. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons.

Drawing models with electrons Place the protons and neutrons in the nucleus. Draw shells (circles) around the nucleus depending on the number of electrons. The first shell can hold up to 2, the rest of the shells hold up to 8 electrons. Don’t pair the electrons until you have gone around once.

Your turn to show what you have learned:

Electron Arrangement The 1st shell can hold up to 2 electrons, and each shell thereafter can hold up to 8 electrons.

Valence Electrons

Valence electrons Electrons in the outermost shells are called Valence electrons. Valence electrons can be gained, lost, or shared during a chemical reaction. Carbon, atomic number 6 6 protons (+) 6 electrons (-) 4 valence electrons Nucleus e- 6 p (+) 6 n

G1 G2 G13 G14G15G16 G17G18 We are not working with Groups Number of valence electrons in each group 1

Valence Electrons Show Smart Notebook animation of valence electrons. File name: Periodic Table of the Elements.

Why are the valence electrons important????

How atoms bond to form compounds has to do with their valence electrons and their energy levels. The number of valence electrons in each atoms helps determine the chemical properties of that element. Atoms tend to be more stable if they have 8 valence electrons (except H and He which are full with 2 e-).

Why are the valence electrons important???? Atoms tend to be more stable if they have 8 valence electrons (except H and He which are full with 2 e-). The number of valence electrons show you how many more are needed to reach 8.

Why are the valence electrons important???? Atoms tend to be more stable if they have 8 valence electrons (except H and He which are full with 2 e-)

C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons

We are not working with Groups 3-12

How to Draw Electron Dot Diagram

What you’ve already learned in class and from readings You learned that Electrons can exist in different energy levels You learned that the # of Electrons in an atom are equal to the # of Protons in an atom You learned that the # of Valence Electrons are the outermost Electrons of an Atom

Valence Electrons Valence electrons are the outermost electrons. The number of valence electrons in each atom helps determine the chemical properties of that element. They are involved in bonding.

Valence Electrons and Electron Dot Diagram Lewis structures, or dot diagrams, are a simplified way to show how the valence electrons are arranged in the outer shell. The # of Valence e- an atom has is dictated by the Group the Element is in. Groups are the Vertical Columns on the Periodic Table!

Electron Dot Diagram For an electron dot diagram, all you have to do is draw dots around an Element’s Symbol But How Many???? dots

Electron Dot Diagram To determine how many valence electrons (dots): 1)Find your element on the periodic table. The Group tells you the number of valence electrons. 2)Determine the number of valence electrons, this is how many dots you will draw around the chemical symbol. 3)Draw the dots around the chemical symbol. 4)You can NOT pair up the electrons unless you have gone around once.

Electron Dot Diagram Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons.

Groups - Review Each column is called a “group” or family. Each element in a group has the same number of electrons in their outer orbital, also known as “shells”. Except for He, it has 2 electrons The electrons in the outer shell are called “valence electrons”

Practice: The First Two Are Tricky so pay attention

Practice: All Elements in the first group have only 1 Valence e-

Practice: All Elements in the first group would have an electron dot diagram like this: H

Practice: All Elements in the second group have only 2 Valence e-

Practice: But what about Helium!!! It only has 2 e- so it can only have 2 e- in its Valence Shell

Practice: All Elements in the second group would have a an electron dot diagram like this He

So… Group 3 3 Valence e- Structure like this: B

Now you should know 1.How many Electrons are found in any Element’s Valence Shell 2.How to draw a Lewis Structure (Electron Dot Diagram)

Assignment: Electron Dot Diagrams Draw electron dot diagrams for the first 20 elements (by order of atomic number).

Electron Dot Diagram 1) Write the element symbol. 2) Carbon is in the 14 th group, so it has 4 valence electrons. 3) Starting at the right, draw 4 electrons, or dots, counter- clockwise around the element symbol.

1) Check your work. 2) Using your periodic table, check that Carbon is in the 4 th group. 3) You should have 4 total electrons, or dots, drawn in for Carbon. Electron Dot Diagram

Electron Dot Diagrams

Do this in your CNB Yes, copy the question! Learning Check 1. X would be the electron dot diagram for A) NaB) K C) Al 2. X would be the electron dot diagram A) BB) N C) P There may be more than one answer.

Bonding and Reactivity The goal of atoms is to have a complete shell with 8 valence electrons (octet rule). (Except H and He which are full with 2 e-) They become stable (happy) when they have their outer shell full. To accomplish a complete shell, atoms bond by transferring or by sharing valence electrons. Transferring occurs by gaining or losing.

Bonding and Reactivity Metals React by losing their valence electrons. In general, their reactivity depends on how easily its lose valence electrons. The reactivity of metals decreases from left to right across the periodic table. Non-metals Non-metals atoms become stable (happy) whey they gain or share enough electrons to have 8 valence electrons (full shell). Metalloids Atoms of the metalloids can either lose or share electrons when they combine with other elements.