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THE STRUCTURE OF MATTER Chapter 5. Section 1 Compounds and Molecules.

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Presentation on theme: "THE STRUCTURE OF MATTER Chapter 5. Section 1 Compounds and Molecules."— Presentation transcript:


2 Section 1 Compounds and Molecules

3 What Are Compounds?  What is a compound?  What is an example of a compound?  What are chemical bonds?  The attractive force that holds atoms or ions together.

4 What Are Compounds?  Chemical formula  A combination of chemical symbols and numbers to represent a substance.  Shows the types and numbers of atoms or ions making up the simplest unit of the compound.  Compounds will always be made of the same elements in the same proportion.  What are some examples of chemical formulas that you know?

5 What Are Compounds?  Chemical structure-  Tells us the arrangement of atoms in a substance.  How the atoms in the compound are arranged determines many of the compounds properties.  Bond length  Give the average distance between the nuclei of two bonded atoms.  Bond angle  The angle formed by two bonds to the same atom.  How the atoms are arranged in space.

6 Models of Compounds  Models help us to see what a compounds structure looks like.  Some can give an idea of bond lengths and angles.  There are three models that are used to represent the arrangement of compounds.  Space filling  Ball and stick  Structural formulas

7 Models of Compounds  Space filling  Shows the space occupied by the atoms.  In this type of model, it is hard to see the bond lengths and angles.

8 Models of Compounds  Ball and Stick  This type of model helps us in seeing a compounds structure.  Shows how the atoms or ions are arranged.

9 Models of Compounds  Structural Formulas  A formula that indicates the location of the atoms, groups, or ions relative to one another in a molecule.  Indicates the number and location of chemical bonds.  Only shows the chemical symbols that represent the atoms.

10 Lewis Dot Diagrams, For Compounds  Draw the diagram for each element listed in the compound.  Draw the elements close together so that where there are electrons missing, or single electrons, each can line up and bond.  Draw a line attaching the atoms together, making sure that all of the atoms have 8 electrons.  Exception for Hydrogen and Helium.

11 How Does Structure Affect Properties?  The strength of attractions between molecules varies.  Properties between molecules can very differently from one another depending on the structure of the molecules or compounds.  Compounds can vary in properties depending on the state at which the compound is at when at room temperature.

12 How Does Structure Affect Properties?  Attractions between water molecules are called hydrogen bonds.  What is a hydrogen bond?  The intermolecular forces occurring when a hydrogen atom that is bonded to a highly electronegative atom of one molecule is attracted to two unshared electrons of another molecule.  Occur between oxygen of one atom and the hydrogen of another atom.

13 How Does Structure Affect Properties?  Hydrogen bonds  Have a higher boiling point than other compounds bonded to hydrogen.  Bonds are stronger connecting within each molecule than the bonds connecting between the water molecules.

14 Section 2 Ionic and Covalent Bonding

15 What Holds Bonded Atoms Together?  Atoms bond in different ways to form many substances.  The type of bonds formed between atoms affect the substances properties.  What bonds atoms?  Electrons

16 What Holds Bonded Atoms Together?  Atoms bond when their valence electrons interact.  Join to form bonds so that each atom has a stable electron configuration.  If the electron configuration is “stable”, its electronic structure will be similar to what?  A noble gas

17 What Holds Bonded Atoms Together?  When atoms bond, the attraction between the nucleus of one atom and the electron of the other atom pull the two atoms together.  By pulling together, the electron clouds overlap and form a bond.  The bond will not break apart unless there is enough energy added to break the bond.

18 What Holds Bonded Atoms Together?  Bonds between atoms can bend and stretch without breaking.  Hold atoms tightly together, but can move back and forth.  Nuclei can change their distances between each other.  Bond lengths are given as averages due to this bending and stretching.  Think of the bonds as flexible springs.

19 What Holds Bonded Atoms Together?  There are three different kinds of bonds that describe the way atoms bond:  Metallic bonds  Covalent bonds  Ionic bonds

20 Metallic Bonds  What are metallic bonds?  A bond formed by the attraction between positively charged metal ions and the electrons around them.  Nucleus of one atom is attracted by the electron cloud of another metal atom. Due to the attraction, the atoms are closely packed with each other, causing the outermost energy level to overlap.

21 Metallic Bonds  Overlapping of electron cloud causes the electrons to be able to move from one atom to another.  The movement of the electrons help in explaining why metals can conduct electricity well.  Why are metals flexible?  The atoms can slide past each other without breaking bonds.

22 Ionic Bond  What is an ionic bond?  A bond formed by the attraction between oppositely charged ions.  Basically, a metal and a nonmetal bonding together.

23 Ionic Bonds  Ionic bonds are formed by the transfer of electrons.  One atom will give up or lose its electron or electrons and the other atom will gain the electron or electrons.  Each ion that is formed will have a stable electron configuration.  The cation and anion formed, attract each other and form an ionic bond.

24 Ionic Bonds  When these compounds are melted or dissolved in water, they conduct electricity.  How do we get a current? What is moving or going on to cause this current?  Moving charges. Melting or dissolving an ionic compound breaks the bonds and the ions break apart.  Ions are then floating in the solution moving charge throughout.

25 Ionic Bonds  Do ionic compounds have a high or low melting point?  High melting point because the ions are holding the structure together tightly and will take a lot of energy to break the bonds.

26 Naming Ionic Compounds  How are ionic compounds formed?  Between cations and anions  When naming the compounds, the cation is named first, and has the name of the element.

27 Naming Ionic Compounds  The names of the anions are named second and are altered.  The ending of the anion changes to –ide.

28 Naming Ionic Compounds  How we write chemical formula’s for ionic compounds is by going by the charge on the cation and anion.  We find the charges on the periodic table how?  Charges are found by looking at the periodic table and seeing how many valence electrons each atom has.  Metals all have a what kind a charge?  Nonmetals all have what type of charge?

29 Naming Ionic Compounds  We cannot determine the charges of the transition metals from the periodic table.  Transition metals can have multiple charges due to the electrons being able to rearrange themselves into the orbitals differently.  Allows them to form different numbers of bonds.

30 Naming Ionic Compounds  Transition metals use roman numerals to state what charge is on the element.

31 Writing Formulas for Ionic Compounds  When we have an ionic compound, we can determine the charge by using the “Criss-Cross” Method.  This method can be used even when there is not a transition metal.  An exception that we will have to look for is if the chemical formula has been simplified.

32 Covalent Bonds  What are covalent bonds?  A bond formed when atoms share one or more pairs of electrons.  These compounds are made up of two or more nonmetals. Two or more elements on the right side of the periodic table.

33 Covalent Bonds  Most covalent compounds have low melting points below 300ºC, but there are some exceptions.  Most molecules remain intact and do not conduct electricity when they are not molecules, why?  They are not comprised of charged ions when the bonds are broken.

34 Covalent Bonds  Atoms joined by covalent bonds share electrons.  They do not transfer between atoms because they both need to gain electrons to form a full outermost energy shell.

35 Covalent Bonds  Atoms can share more than one pair of electrons.  Single bond- when a pair of electrons bond, one line connecting two atoms.  Double bond- when 2 pairs of electrons bond, two lines connecting two atoms.  Triple bond- when 3 pairs of electrons bond, three lines connect two atoms.

36 Covalent Bonds  As we increase from a single to a triple bond, we are increasing in energy. Why?  The distance between the atoms is shorter. Atoms are held more tightly. More energy is needed to break the bonds. Single is easiest and triple is more difficult.

37 Naming Covalent Compounds  Prefixes are used to denote how many of each atom are present in the chemical formula.  The element that is furthest on the right on the periodic table is named second and has its ending changed to – ide.

38 Polyatomic Ions  Some compounds have both ionic and covalent bonds.  Polyatomic ions  An ion made of two or more atoms.  Groups of covalently bonded atoms that have either lost or gained electrons.

39 Polyatomic Ions  These ions have a set formula that they are known by.  When writing polyatomic ions, parenthesis are put around it to remind that it acts like a single ion.  The charge for a polyatomic ion is for the entire ion, not just one specific atom in the ion.

40 Polyatomic Ions  Some polyatomic anion names relate to their oxygen content.  Most of the polyatomic ions that contain oxygen have the endings –ite and –ate.  Does not tell how many oxygens are in the polyatomic ion, but helps in learning the pattern.  Polyatomic with more oxygens has the –ate ending.  Example, Sulfate: SO 4  Polyatomic that has fewer oxygens has the –ite ending.  Example, Sulfite: SO 3

41 Section 4 Organic and Biochemical Compounds

42 Organic Compounds  What is an organic compound?  A covalently bonded compound that contains carbon, excluding carbonates and oxides.  These compounds always contain carbon and almost always hydrogen.  Oxygen, nitrogen, sulfur and phosphorous can be found in organic compounds as well.

43 Organic Compounds  Carbon atoms form four covalent bonds in organic compounds. Why?  Form four bonds because they have four valence electrons.  When a compound is made of only carbon and hydrogen, we call this a hydrocarbon.

44 Organic Compounds  Methane is the simplest hydrocarbon and it is formed when living matter, like plants, decay.  Organic compounds to know:  Methane CH 4  Ethane C 2 H 6  Propane C 3 H 8  Butane C 4 H 10  Carbon can form single, double and triple bonds, but it can never have more than four bonds to an atom.  Can never have more than 8 total electrons.

45 Organic compounds  Alkanes are hydrocarbons that only form single bonds.  When the hydrocarbon chain has more than 3 carbons, the hydrocarbon can rearrange itself in three different ways:  Branched, unbranched or rings.  Alkanes follow a pattern when writing chemical formulas, except for the ring structures.  C n H 2n+2  Carbon chains can go onto having double and triple bonds and have specific names.

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