electrons.ppt

8/13/2019 electrons.ppt

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The groups, and electron dot

diagrams


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Elements can be divided into groups, orfamilies.

Element Families

Why do atoms combine?

1

Each column of the periodic table containsone element family.

Hydrogen is usually considered separately,so the first element family begins withlithium and sodium in the first column.


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Element Families


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Just as human family members often havesimilar looks and traits, members of elementfamilies have similar chemical properties

because they have the same number ofelectrons in their outer energy levels.


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Neon and theelements below it inGroup 18 have eightelectrons in their

outer energy levels.

Noble Gases


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Their energy levelsare stable, so they

do not combineeasily with otherelements.


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At one time these elements were thoughtto be completely unreactive, and thereforebecame known as the inert gases.

Noble Gases


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When chemists learned that some of thesegases can react, their name was changed tonoble gases. They are still the most stable

element group.


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The elements inGroup 17 are calledthe halogens.

Halogens


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Fluorine is themost reactive ofthe halogensbecause its outer

energy level isclosest to thenucleus.


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Halogens


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The reactivity ofthe halogensdecreases downthe group as the

outer energylevels of eachelements atoms

get farther fromthe nucleus.


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Alkali Metals


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The alkali metals form compounds thatare similar to each other.

Alkali Metals


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Alkali metals each have one outer energylevel electron.

It is this electron that is removed whenalkali metals react.

The easier it is to remove an electron, themore reactive the atom is.

Unlike halogens, the reactivities of alkalimetals increase down the group.


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If you want to see how atoms of one elementwill react, it is handy to have an easier wayto represent the atoms and the electrons intheir outer energy levels.

Electron Dot Diagrams


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You can do this with electron dot diagrams.

An electric dot diagramis the symbol for

the element surrounded by as many dots asthere are electrons in its outer energy level.


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The dots are written in pairs on four sides ofthe element symbol.

How to Write Them


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Start by writing one dot on the top of theelement symbol, then work your way around

adding dots to the right, bottom, and left.


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How to Write Them


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Add a fifth dot to the top to make a pair.Continue in this manner until you reacheight dots to complete the level.


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Now that you know how to write electrondot diagrams for elements, you can use themto show how atoms bond with each other.

Using Dot Diagrams


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A chemical bondis the force that holds twoatoms together.

Atoms bond with other atoms in such a waythat each atom becomes more stable. Thatis, their outer energy levels will resemblethose of the noble gases.


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1

Section Check

Question 1

Electrons are now known to swarm around thenucleus of an atom in a configuration known as

the _______.

A. electron circle

B. electron cloud

C. electron configurationD. electron swarm


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Section Check

Answer

The answer is B. The cloud includes all the

regions where an electron might be found.


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Section Check

Question 2

What information can you learn from thisdiagram?

S C


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Section Check

Answer

This image is an example of an electron dot

diagram. It tells you that nitrogen contains five

electrons in its outer energy level.

S ti Ch k


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1

Section Check

Question 3

The _______ an energy level is from the

nucleus, the _______ electrons it can hold.

A. closer, more

B. closer, less

C. farther, less

D. farther, more

S ti Ch k


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Section Check

Answer

The answer is D. The farthest shells contain the

greatest number of electrons.


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