Going Subatomic!T E K S : 5 B I D E N T I F Y T H AT P R O T O N S D E T E R M I N E A N E L E M E N T ’ S I D E N T I T Y A N D VA L E N C E E L E C T R O N S D E T E R M I N E I T S C H E M I C A L P R O P E R T I E S , I N C L U D I N G R E A C T I V I T Y

Questions and goals:

Questions we have:

How do protons determine an element’s identity?

How do valence electrons determine chemical properties?

Students will be able to:

Identify that protons determine an element's identity and valence electrons determine its chemical properties, including reactivity

A Historical Perspective:

Let’s take a look at the different ideas that scientists have had about atoms over time.

The Bohr Model (of the atom)Depending on what scientists need to observe or study about atoms, they may use a model

The model they actually choose to use depends on what they want to study

If you want to look at how electrons behave, often the Bohr model is used.

The Bohr model is also going to be used to show the number of protons, neutrons and electrons

Quantum or Cloud Model (of the atom)

◦ The cloud is just the name given to the space that electrons are found in.

◦ As an electron gains more energy, it can “jump” to a higher level (shell)

◦ If an electron looses energy, it goes

down (towards the nucleus)

◦ Gains energy – away from nucleus

Relative Sizes in an Atom

The electrons take up most of the SPACE of an atom

But the nucleus = protons and neutrons, make up 99.9% of the MASS of that atom

ProtonsHOW DO PROTONS DETERMINE AN ELEMENT’S IDENTITY?

Protons are important

Recall that protons are one of the 3 main subatomic particles within an atom

It has a positive charge and makes up part of the mass of the atom

All protons are identical.

For example, hydrogen protons are exactly the same as protons of helium and all other elements, or pure substances.

Protons are important

However, atoms of different elements have different numbers of protons.

For example - a hydrogen atom has just one proton, whereas a helium atom has two protons.

The number of protons in an atom determines the electrical charge of the nucleus. So a hydrogen atom would have a +1 charge

Number of Protons = Element Identity

The number of protons an element also us gives the atomic number

For example – if an element has 2 protons, it is helium. If it has 46 protons, the element is palladium

palladium

What makes up a proton?

Quarks!

Protons are made from three quarks (two up quarks and a down quark) that are held together with gluons

Although protons were discovered almost 100 years ago, the quarks and gluons inside them were discovered much more recently. Scientists are still learning more about these fundamental particles.

Summarize your understanding

Answer these questions on your page:

1. Describe protons.

2. What is the relationship between protons and elements?

3. If an atom has three electrons, infer how many protons it has.

4. Identify the fundamental particles that make up a proton.

ElectronsHOW DO VALENCE ELECTRONS DETERMINE CHEMICAL PROPERTIES?

What are Electrons?

Recall that electrons are one of the 3 main subatomic particles within an atom

It has a negative charge and exists outside of the nucleus in the electron cloud

All electrons are identical, no matter which element that are a part of

The electron is most important in the chemical properties of atoms. It is the smallest charged particle we know of and is very stable.

What makes up an electron?

There is no evidence that electrons can be sub-divided. They appear to be pure, primary particles.

Electrons are not made up of quarks. They are in a separate "family" of particles known as LEPTONS.

How do electrons move?

Electrons are important

Electrons are important for the bonding of individual atoms together.

If electrons didn’t bond, none of the substances in our universe would exist!

This interaction between the outer electron layers of an atom is called atomic bonding

How quickly or even explosively atoms bond is known as the “reactivity” of an element

What is “Reactivity”?

What is this really?

Chemical reactivity occurs when substances change chemically.

What is most often produced from this type of change is something in the form of energy, such as heat and combustion.

Watch this!

Information about Reactivity

1. In METALS reactivity DECREASES as you go ACROSS a Period because though they still want to give away valence electrons they have more of them to get rid of, which requires more energy.

2. DOWN a Group: In METALS reactivity INCREASES as you go DOWN a Group because the farther down a Group of metals you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity.

Find your PT from last class!

Add Information about Reactivity to PT

Most reactive metal?

Cesium!

How do we model the electron?Bohr models shows atoms’ electrons organized into energy levels.

Each energy level can hold a specific number of electrons (Note – energy levels are also called orbitals or shells)

Level 1 – holds 2 electrons

Level 2 – holds 8 electrons

Level 3 – holds 8 electrons

Many atoms have additional energy levels

Electrons are not added to energy levels until the lower levels are filled

Bohr Model with levels shown

Outermost level = valence electrons

There are as many energy levels as the atom needs.

The energy level shown furthest from the nucleus is called the outermost energy level.

Again, the electrons found here are called “valence electrons”

Different atoms have a different number of valence electrons

The group number on the periodic table is equal to the number of valence electrons that an element has

Valence Electrons and Reactivity

• When two atoms approach each other and react with each other, it is their outer shells that come into contact first, these electronsin their outer shells that are involved in any chemical reaction.

Valence Electrons and Reactivity

• It is the number of electrons in an atom’s outer shell that determines, how that element will react chemically.

• Each atom wants to be stable with 8 electrons in the outermostshell.

• Chemical bonding takes place in an effort make them more stable

Valence Electrons and Reactivity

The periodic table is arranged such that elements in the same column have the same number of electrons in their outer shell.

Now add this (to PT):

Group number = number of valence electrons!

Video: How to find the number of valence electrons

Summarize your understanding

Answer these questions on your page:

1. Why are electrons important?

2. What are valence electrons?

3. How can you find the number of valence electrons using the periodic table?

Practicing the Bohr Atomic Model

Remember, when you look at an element’s square of the Periodic Table, you can determine the subatomic particles using APE MAN. Once you know the subatomic particle numbers, you can make a Bohr model!

Have this page out to help you:

Practicing the Bohr Atomic Model

Let’s make a Bohr model of Fluorine:

Bohr Diagrams – how to know how many circles to draw

• Find out which period(row) your element is in.

• Elements in the 1st period have one energy level.

• Elements in the 2nd periodhave two energy levels, and soon.

• Energy levels are drawn withcircles

www.chem4kids.com

Bohr Diagrams Practice –adding electrons (the dots)

1) Find carbon on the periodic table.

2) Determine the number of electrons – it is thesame as the atomic number.

3) This is how many electrons you will draw.

Bohr Diagrams – putting the circles and dots together!

C

1) Part of the model has beendone for you.

2) Carbon is in the 2nd period, so ithas two energy levels, or shells.

3) You would draw the number of shells around the nucleus, but this has been done for you.

Bohr Diagrams

1) Add the electrons.

2) Carbon has 6electrons.

3) The first shell canonlyhold 2 electrons, so add those first.

C

Bohr Diagrams

1) Since you have 2 electronsalready drawn, you need to add4 more (for a total of 6).

2) These go in the 2nd shell.

3) Add one at a time - starting on theright side and going counter clock-wise.

C

Bohr Diagrams

1) Check your work.

2) You should have 6 total electrons forCarbon.

3) Only two electrons can

fit in the 1st shell.

4) The 2nd shell can hold up

to 8 electrons.

5) But carbon only has 6 total, so this energy level will not be full.

C

Bohr DiagramsTry the rest of the elements with your table partner:

a) H

b) O

c) Mg

d) Cl

e) Si

C