Physical Science Chapter 6 Chemical Bonds. Bonding Chapter 6 is about different types of atomic...
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Transcript of Physical Science Chapter 6 Chemical Bonds. Bonding Chapter 6 is about different types of atomic...
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
• http://www.youtube.com/watch?v=QXT4OVM4vXI
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?
+=
How will we combine these elements?
+ = MgCl2
•MgCl2 = 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, H2O has a hydrogen to oxygen ratio of 2:1
• Find the ratios of the following formulas:• Sodium Chloride, NaCl=• Magnesium Chloride, MgCl2=
• Sodium Oxide, Na2O=
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
• http://www.youtube.com/watch?v=yjge1WdCFPs
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 H2
• 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
• http://www.youtube.com/watch?v=QqjcCvzWwww
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
• http://www.youtube.com/watch?v=PVL24HAesnc