Chapter: Atomic Structure and Chemical Bonds

Table of Contents

Section 1: Why do atoms combine?

Section 2: How Elements Bond

Chapter: Atomic Structure and Chemical Bonds

Table of Contents

Section 1: Why do atoms combine?

Atoms combine in different arrangements to form all the substances we know.**Atoms combine to have a stable electron arrangement.

What you will learn:How electrons are arranged in an atom That the electron arrangement is important to the properties of this atom and to the capability of reacting with other atoms.

This information will help us understand chemical reactions

1)The nucleus: represents most of the mass2) The electron cloud with electrons that are very small and mostly empty space 3) Nucleus very smallcompared to the electroncloud.

The atom has:

• Nucleus has (+) charge = protons• Electrons have a (-) charge and move

randomly in the electron cloud

Atoms Charges

** Element Structure is the specific number of protons, neutrons, and electrons in an atom and how the electrons are distributed in the electron cloud**Element Structure will determine the chemical and physical properties of the atoms and how atoms react with other atoms.

What is Element Structure or Element Configuration ?

The electron cloudhas severalenergy levels.Electrons will move from one energy level toanother.Each level has a different amount of energy

Electron Arrangement

Energy levels are also called shells, valence shells

Each energy level can hold a different number of electrons ( 2, 8, 18 …) – some exceptions

Energy Levels and Number of electrons

• Electrons are attracted by the nucleus - so USUALLY the electrons will occupy the energy levels closer to the nucleus first.

Energy Levels

**The electrons in the outermost energy level always have the greatest energy and are less stable. **Less stable means that this atom will react easily with other atoms.**The force that attracts them to the nucleus is much weaker because it is an area far from the protons.

***The electrons that occupy the last energy level are called valence electrons and are the electrons involved in chemical reactions

Valence Electrons in the Periodic table Groups handout with note taking wkst

Elements in Group 1: 1 valence electron Group 2: 2 valence electronsGroup 13: 3 valence electronsGroup 14: 4 valence electronsGroup 15: 5 valence electronsGroup 16: 6 valence electronsGroup 17: 7 valence electronsGroup 18: 8 valence electrons – except for helium, which has 2 (these are all stable)Groups 3 -12 changes

2n2 – formula used to calculate the maximum number of electrons an energy level can holdn = the number of the energy level.

Energy Levels

Octet Rule

** Octet Rule states that:An atom with 8 electrons on the last energy level is considered stable.There are exceptions – Helium and Hydrogen need 2 ( these atoms have one energy level only – page 467 fig 5)

*In MANY CASES: if the last energy level is complete, the atom is stable

Atoms will react with other atoms to become stable, forming molecules.A chemical bond is the force that holds two atoms together.

**3 ways an atom can combine with others and became stable: An atom can gain, donate, or share electrons.

-Atoms with 1, 2 or 3 electrons in the outer energy level – will lose electrons to become stable (atoms in groups 1,2 and 3)-Atoms with 5, 6 and 7 electrons in the outer energy level, will receive electrons to become stable (atoms in groups 5,6 and 7)- Atoms with 4 usually share electrons

EX: The atoms in Group 1 need to donate one electron and the atoms in the Group 17 need to receive one electron.They are the most reactive in the periodic table and often react with each other forming salts.

•Group 1 – Alkali Metals•Group 17 – Halogens

Representing Atomic Configuration or Structure •There are 2 ways we can represent the electron configuration of atoms:•Bohr Model of the atom as seen on page 467 •Lewis Structure also called Electron Dot Diagram

Lewis Structure or Electron Dot Diagram

Bohr Model of the atom

Atom Diagrams

“Bohr Model”, shows the distribution of all the electrons of an atom

How to do the Bohr Model:Ex: Oxygen- Find the atomic number- Find the number of electrons- Distribute the electrons in the

energy levels- check the list of valence electrons to see if it is correct

Draw the Bohr model for Sodium, Phosphorus, Fluorine and Hydrogen

Sodium

Let’s do the Bohr Model for Phosphorus,Fluorine and Hydrogen

Phosphorus atomic number - 15

Fluorine Atomic number - 9

Hydrogen atomic number = 1one electron in the last shell, very

reactive

• Electron dot diagram or Lewis Structure - shows how the electrons are distributed in the last energy level.

• They are useful to represent chemical reactions among atoms.

Let’s do it for NEON

Steps to do an Electron Dot Diagram:

• Find the group the atom belongs to in the PT

• Refer to your “Number of Valence Electrons per group”handout and find out the number of valence electrons in an atom of that element

• The dots are written in pairs on four sides of the element symbol.

• Start by writing one dot on the top of the element symbol, then work your way around adding dots to the right, bottom, and left.

Valence Electrons Group 1: 1 valence electron Group 2: 2 valence electronsGroup 3: 3 valence electronsGroup 13: 3 valence electronsGroup 14: 4 valence electronsGroup 15: 5 valence electronsGroup 16: 6 valence electronsGroup 17: 7 valence electronsGroup 18: 8 valence electrons – except for helium, which has 2

CHAPTER 16 - SECTION 2

• How elements bond:Chemical bond is the force that

keeps two atoms together.• We already studied that:Atoms can gain, donate or share

electrons

• There are 3 types of bonds between atoms

Ionic Bonds Covalent Bonds Metallic Bonds

In Ionic Bonds: one atom gives an electron, the other receives

In Covalent Bonds: atoms will share electrons

**Bonds

• Atoms form bonds with other atoms using the electrons in their outer energy levels.

• Atoms form bonds so both atoms will have an stable atomic structure

• Atomic Stable Structure means that the outer energy level of that atom is complete or has 8 electrons.

Symbols for Compounds

• Elements are represented by symbols and these symbols are letters

• molecules are represented by symbols and numbers. (molecules are combinations of atoms)

Ex: H2O – 2 atoms of Hydrogen and one of oxygenThe number “2” is called a subscriptH2O is called a chemical formula (for water)

Chemical Formulas – Importance of the subscript

CO – carbon monoxide / CO2 – carbon dioxide

Water – H2O / Hydrogen Peroxide - H2O2

**IMPORTANT TO REMEMBER

• Ionic bonds – bonds between metals and nonmetals or metalloids, forming Ionic Compounds

• Covalent bonds – bonds between nonmetals or metalloids, forming molecular compounds

• Metallic bonds – bonds between metals, forming metallic compounds

Ionic Bonds—Loss and Gain

Sodium has only one electron in its outer energy level.

Removing this electron empties this level and leaves the level below complete, and the atom is stable

Ionic Bonds—Loss and Gain

By removing one electron, sodium becomes stable and becomes a positive ion : Na+( lost one negative charge - not neutral anymore)

Ions Formation Na+ and Cl-

- Sodium becomes a + ion - Chlorine becomes a – ion (receives one electron

from Sodium)- Na and Cl combine forming NaCl (sodium

chloride)

Chemical Reaction representation using the Electron Dot Diagram

This is Ionic Bond and NaCl is an ionic compound.

More Gains and Losses

Can elements lose or gain more than one electron?

Mg can lose 2 and Oxygen can gain 2 electrons to become stable.

When this happens, magnesium oxide (MgO) is formed and is an ionic compound

More Gains and Losses

• Can elements lose or gain more than one electron?

EX: Magnesium and Oxygen1) where can you find these atoms in the PT? Which Groups?2) How many electrons do they have in the outer energy level?3) Which one will lose and which one will gain?

Practice: Ionic bonds

Show the transfer of electrons in the following combinations

Na + Cl Mg + BrCl + Ca Ca + OK + F K + OMg + I Be + SAl + Br Na + OFe + O ( Fe has 2 valence electrons)Cu + Cl ( you will have to do the Bohr Diagram of Cu to find out the number of valence electrons)

Covalent Bonds— electron sharing

• because of the number of electrons in their outer levels, some atoms will share electrons

• Covalent Bonds happen between nonmetals

The Covalent Bond

Covalent bond – atoms share the electrons in the last energy level

During covalent bonding a molecule or a molecular compound is formed

3 types of Covalent bonds: single, double and triple

6 and 4 atoms are too many to donate or gain – so these atoms will share electrons

Double Bond – CO2

Triple Bond

N has 5 e- in the last energy level

Show how the pairs of atoms below share electrons. They can share 1,2 or 3 electrons

in order to become stable

1)H+H 6)F+F2)O+O 7)N+N (N2)

3)C+O (CO2) 8)H+O (H2O)

4)N+O (N2O2) 9)S + O

5)H+F 10)N + H (NH3)

Metallic Bonding

They are free to move from one atom to another creating a “sea of electrons” or a “shared pool of electrons”.

Metals share electrons in a special way. Electrons are not bonded to any particular atom.

Metallic Bonding is responsible for many of the metals properties such as: being good conductors of electricity and being malleable.

Metals share electrons in a special way. Electrons are not bonded to any particular atom.

According to what you know about the different groups in the periodic table:

-Which Groups of atoms will donate electrons? Which Groups will receive electrons??? You can use the valence electrons list to answer.

-What are the types of atoms that will combine with ionic bonds?

-What types of atoms will form Metallic bonds? -What type of atoms will share electrons in Covalent bonds?

According to what you know about the different groups in the periodic table:-Which Groups of atoms will donate electrons? Groups 1,2,3-Which Groups will receive electrons??? Groups 15, 16 and 17-What types of atoms will form Ionic Bonds? metal and nonmetals-What types of atoms will form Metallic bonds? atoms of metals -What type of atoms will share electrons in Covalent bonds? Nonmetal and Nonmetal

**Covalent bonds can be:Polar and Nonpolar bonds

• Sometimes atoms will not share the electrons equally.

• This happens because some atoms attract the electrons more than others

Non Polar – electrons in the bond are shared equally

Polar – electrons in the bond are not shared equally

Electronegativity

Electronegativity is the tendency of an atom to attract a bonding pair of electrons.

Polar Bond - the shared pair of electrons stay “closer” to the atom that has a stronger pull (more electronegative)Molecule will have a + and a – side ( weak charge)

EX: Water Oxygen has a higher electronegativity than Hydrogen. H2O – in water hydrogen and oxygen are united by a polar bond

EX: Water is a polar molecule

If a molecule has an uneven distribution of electrons this molecule is called polar.The atoms are united by polar covalent bonds

In a water molecule, the electrons spend more time around the oxygen atom.This molecule has a weak charge

Carbon Dioxide: Nonpolar Molecule

• If a molecule has an even distribution of electrons it is called nonpolar.

• This molecule have no charge • The bond that keep the atoms together

is called a nonpolar bond

Nitrogen molecule is nonpolar

Why is water considered the universal solvent?

• Because of its polarity ( weak charge), water has the ability to dissolve most compounds ( more than any other solvent)

Like dissolve like???

• Polar solvent will dissolve polar solutes

• Nonpolar solvents will dissolve nonpolar solutes

• Water can dissolve polar solutes and also ionic compounds because of its charge

*Water and Oil – Oils Spills

• *Why water and oils do not mix?

• *Because one molecule is polar and the other is nonpolar.

• How do detergents work?

Follow the principle Like dissolves like

Water and Oil• Surfactants or Dispersants are

molecules that have one side that is polar and one nonpolar. Ex Detergents

• Detergents will break oils into small droplets making it easier to wash away.

The polar side is Hydrophilic – attracted to the waterThe non-polar side Hydrophobic- attracted to the oil

• This can be important in the case of oil spills

Oil spills and some methods to clean it

Method 1 – Booms and Skimmers – floating devices

that contain the oil

Containment of oil with booms

Recovery: use of floating devices called skimmers - are sponges that will absorb the oil

Method 2: Burning: problem smoke

Method 3: Sorbents

Method 4: Shoreline clean up

Method 5: Surfactants or Dispersants

*Detergents are called surfactants or dispersants and will break oil into small droplets. *Small droplets of oil are easier to disperse in water, and are more rapidly degraded by microbes

the smaller the droplets the faster they are consumed by bacteria and the

faster the oil will be removed from the area

Dispersants

Small oil droplets will be consumed by bacteria