Physical Science Chapter 6 Chemical Bonds

Bonding Chapter 6 is about different types of atomic bonding Forces of attraction is the key to this bonding The physical properties of elements is key to the different types of bonds

Bonding

Draw the electron configuration of the elements neon and sodium

What do you notice about the Valence electrons and the energy level of each element?

Stable Electron Configurations When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react

Ionic Bonds Elements without complete sets of valence electrons tend to react They react to try to achieve the stability of a full energy level…like the noble gases

Transfer of Electrons Look at the electron dot diagrams for sodium and chlorine What do you think these elements will want to do?

Atomic Chemical Reaction When sodium and chlorine react: An electron is transferred from each sodium atom to a chlorine atom. Now each atom is more stable

When an atom gains or loses an electron, the protons and electrons are no longer equal and the atom is not neutral. An atom with a positive or negative charge is an ion

Notice the positive and negative charge on the new sodium and chlorine atoms

Charge An ion with a negative charge is an anion. Chlorine in NaCl is an anion…Cl - It is negative because it has one more electron than protons, thus a charge of 1- Anions are written using a part of the elemental name and the suffix ide. – chloride

Our new sodium ion, because it lost an electron now has more protons than electrons, making it positive or 1+ – Na + Cations are named just using the elemental name, sodium

Chemical Bonds A chemical bond is what holds atoms or ions together Ionic bonds are what holds cations and anions together – Ionic bond forms when electrons are transferred from one atom to another

Chemical Bonds 4vXI 4vXI

Ionization Energy The amount of energy used to remove an electron from an atom is ionization energy It varies form element to element The lower the ionization energy, the easier it is to remove an electron

Which element would it be easier to take an electron from, Magnesium or Calcium?

Ionic Compounds Compounds that contain ionic bonds are ionic compounds These can be represented by a chemical formula: – Notation that shows what elements a compound contains and the ratio of the atoms or ions of these elements in the compound: NaCl

Practice We want to make a compound with magnesium and chloride What group is magnesium in? What group is chlorine in?

How will we combine these elements? + =

+ = MgCl 2

MgCl 2 = The subscript 2 shows how many atoms of that element are present If there is not a subscript, that implies that there is only one atom

Ratios are Easier It is easier to see the number of atoms when you break a formula down into ratios For example, H 2 O has a hydrogen to oxygen ratio of 2:1 Find the ratios of the following formulas: Sodium Chloride, NaCl= Magnesium Chloride, MgCl 2 = Sodium Oxide, Na 2 O=

Crystal Lattices How are the ions in a grain of salt arranged?(162) Attractions between opposing charges keeps the ions in a fixed, repeating position Solids whose particles are arranged in lattice structure are called crystals

The shape of an ionic crystal depends on the arrangement of ions in its lattice The arrangement of the ions depends on the ratio of ions (like the exercise you just did) and their relative sizes

Compare Compare figure 5a and 5b (pg 162) Answer the following questions: 1. How are the sodium ions represented? 2. How are the Chloride ions represented? 3. What do you notice about the locations of the positive and negative ions? 4. What is the similarity between the diagram of NaCl and the photograph of NaCl?

Properties of Ionic Compounds The properties of NaCl are typical of other ionic compounds: High melting point (801 degrees Celsius) As a solid they are poor electric conductors As a liquid they are good electric conductors They shatter when struck with a hammer

All of these properties of ionic compounds are explained by the strong attractions within a crystal lattice

For electric current to flow, charged particles must be able to flow from one location to another Ions in a crystal lattice have a fixed position When they melt, the lattice breaks apart and ions are free to flow Melted sodium chloride is an excellent elctric conductor

Complete the section 1 assessment in your book and the questions in your workbook for this section

Covalent bonds FPs FPs

Covalent Bonds Someone read Covalent Bonds, pg 165 Covalent Bond: a chemical bond in which two atoms share a pair of valence electrons

Example: Hydrogen has one valence electron If it had one more it could reach the stability of a full orbital for its energy level So it wants to share an electron with another atom that also only has one valence electron… Hydrogen

These two hydrogen atoms that share a valence electron form a molecule Molecule: a neutral group of atoms that are joined together by one or more covalent bonds

The molecule is neutral because it has two protons and two electrons The attraction between the shared electrons and the protons in the individual nuclei holds the atoms together in a covalent bond

The chemical formula for this covalent bond/molecule is H 2 The subscript 2 is for the 2 hydrogen atoms in the molecule

Diatomic molecules: Two atoms Many nonmetals make diatomic molecules…why?

Halogens, for example, all have 7 valence electrons If two of them share an electron they both achieve a stable electron configuration

Multiple covalent bonds Atoms can share more than one electron They can share pairs If they share 2 pairs, it is called a double bond If they share 3 pairs it is called a triple pair

Ionic and Covalent bonds www www

Polar Covalent Bonds A covalent bond in which electrons are not shared equally is a polar covalent bond In a molecule with the same element, the attraction is the same In a molecule of a compound, this may not be the case

Some atoms may have a greater attraction than others and thus the electrons spend more time near that atom in the bond than the other

Because they are sharing electrons, neither atom becomes + or – like ionic bonds. However, they can become partially + or – when the electrons are shared unequally If so, they are assigned the symbol delta – or delta +, depending on which one gains or loses the electrons most

Polar and Nonpolar Molecules snc snc

Polar and Nonpolar Molecules *Recall that a molecule is a neutral group of atoms that are joined together by one or more covalent bonds* A molecule that has only two atoms that share a covalent bond, the molecule will be polar A molecule that has more more than two atoms that share a covalent bond, the molecule may not be polar

The type of atom in a molecule and its shape determine whether a molecule is polar or nonpolar

Nonpolar example Carbon dioxide CO 2 Oxygen has a stronger attraction for electrons Therefore it is a polar molecule Because the molecule is linear, However, the equal pull cancels Out the polarity and the Molecule is nonpolar

Polar Example Water, H 2 O Oxygen has a stronger attraction to electrons than hydrogen, making this a polar molecule Because the shape is bent, the polar bonds do not cancel out This is a polar molecule

Attraction Between Molecules Attractions between Molecular compounds are not as strong as ionic or covalent bonds Attractions between polar molecules are stronger than attractions between nonpolar molecules

These strengths and weaknesses explain a lot about elements and their behavior Water and methane are very similar in mass, but methane boils at C and water boils at 100 C

Methane is nonpolar and water is polar These attractions increase the energy required for materials to boil/break the bonds

Activity Create a comparison chart Compare the different bonds we have discussed – 1. ionic bonds – 2. covalent bonds – 3. polar bonds – 4. nonpolar bonds Include how the electrons behave, types of elements involved in the bond, strength of the bond, etc.