Chapter 4 The Structure of Matter How atoms form compounds
Compounds Formed when two or more elements combine Must make a chemical change New properties Atoms from the different elements form bonds Chemical Bond- the attractive force that holds different atoms or ions together
Compounds Every compound has a specific ratio of atoms Written as a chemical formula H 2 O, C 12 H 22 O 12, NaCl The ratio is the same every time, every where Different ratio means a different compound
Chemical Structure Shows how the atoms are arranged in the compound How the atoms or ions are connected In order to specify where we need Bond length- distance between the nuclei Bond angle- Angle between atoms (requires two bonds)
Models Ball and stick- Ball represents atoms, stick represents bonds Easy to see bond angles Structural formulas- drawn with connections between atoms shown. H O H H H C O H H
Models Space-filling Shows that atoms the right size and in the right place.
C 4 H 9 O 2 N
2 Types of structures Networks A large number of atoms, all bonded together Atoms bonded Or ions opposite charges
Network Solids Many atoms all bonded together Quartz is SiO 2 Major component of rocks. Each Silicon bonded to 4 oxygen atoms Angle is 109.5º Gives it a strong rigid structure Makes rocks hard. Gives them a high melting and boiling point
Network Solids Ions bond together Opposite charges attract All the positives get surrounded by negatives Get a repeating pattern Rigid Brittle High mp and bp
Molecules Specific atoms joined together Weaker attractions than ions. Low melting and boiling points Things we know as gases and liquids Stronger attraction- higher melting and boiling temperatures
Bonding When the valence electrons interact Atoms react to achieve full outermost energy levels Two ways to do this Share electrons Transfer electrons
Keeping Track of Electrons Atoms in the same column Have the same outer electron configuration. Have the same valence electrons. Group 1 has 1 valence electrons Group 2 has 2 valence electrons Group 13 has 3 valence electrons Group 14 has 4 valence electrons etc
1 2 Helium only has 2 valence electrons 3 4 5 6 7 8
Electron Dot diagrams A way of keeping track of valence electrons. How to write them Write the symbol. Put one dot for each valence electron Don t pair up until they have to X
The Electron Dot diagram for Nitrogen Nitrogen has 5 valence electrons. First we write the symbol. Then add 1 electron at a time to each side. Until they are forced to pair up. N
Write the electron dot diagram Na Mg C O F Ne He for
Electron Configurations for Cations Metals lose electrons to fill their outer levels They make positive ions.
Electron Dots For Cations Metals will have few valence electrons Ca
Electron Dots For Cations Metals will have few valence electrons These will come off Ca
Electron Dots For Cations Metals will have few valence electrons These will come off Forming positive ions Ca +2
Electron Configurations for Anions Nonmetals gain electrons to fill their outer levels They make negative ions.
Electron Dots For Anions Nonmetals will have many valence.electrons. They will gain electrons to fill outer shell. P P -3
Stable Arrangements All atoms react to fill their outer levels Noble gases have full outer energy levels. 8 valence electrons. Also called the octet rule. Ar
Ionic Bonding Anions and cations are held together by opposite charges. The bond is formed through the transfer of electrons. Electrons are transferred to fill their outer levels
Ionic Bonding Na Cl
Ionic Bonding Na + Cl -
Ionic Bonding All the electrons must be accounted for! Ca P
Ionic Bonding Ca P
Ionic Bonding Ca +2 P
Ionic Bonding Ca +2 P Ca
Ionic Bonding Ca +2 P -3 Ca
Ionic Bonding Ca +2 P -3 Ca P
Ionic Bonding Ca +2 P -3 Ca +2 P
Ionic Bonding Ca Ca +2 P -3 Ca +2 P
Ionic Bonding Ca Ca +2 P -3 Ca +2 P
Ionic Bonding Ca +2 Ca +2 P -3 Ca +2 P -3
Ionic Bonding Ca 3 P 2 Formula Unit
Properties of Ionic Compounds Crystalline structure. A regular repeating arrangement of ions in the solid. Ions are strongly bonded. Structure is rigid. High melting points- because of strong forces between ions.
Crystalline structure
Do they Conduct? Conducting electricity is allowing charges to move. In a solid, the ions are locked in place. Ionic solids are insulators. When melted, the ions can move around. Melted ionic compounds conduct. First get them to 800ºC. Dissolved in water they conduct.
Metallic Bonds How atoms are held together in the solid metal Metals hold onto there valence electrons very weakly. Think of them as positive ions floating in a sea of electrons.
Sea of Electrons Electrons are free to move through the solid. Metals conduct electricity. + + + + + + + + + + + +
Metals are Malleable Hammered into shape (bend). Ductile - drawn into wires.
Malleable + + + + + + + + + + + +
Malleable Electrons allow atoms to slide by. + + + + + + + + + + + +
Ionic solids are brittle + - + - - + - + + - + - - + - +
Ionic solids are brittle Strong Repulsion breaks crystal apart. + - + - - + - + + - + - - + - +
Covalent bonds Nonmetals hold onto their valence electrons. They can t give away electrons to bond. Still want full outer level Get it by sharing valence electrons with each other. By sharing both atoms get to count the electrons toward noble gas configuration.
Covalent bonding Fluorine has seven valence electrons F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons Both end up with full energy level F F
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons Both end up with full energy level F F 8 Valence electrons
Covalent bonding Fluorine has seven valence electrons A A second atom also has seven By sharing electrons Both end up with full energy level 8 Valence electrons F F
Single Covalent Bond A sharing of two valence electrons. Only nonmetals and Hydrogen. Different from an ionic bond because they actually form molecules. Two specific atoms are joined. In an ionic solid you can t tell which atom the electrons moved from or to.
How to show how they formed It s like a jigsaw puzzle. I have to tell you what the final formula is. You put the pieces together to end up with the right formula. For example- show how water is formed with covalent bonds.
Water H O Each hydrogen has 1 valence electron Each hydrogen wants 1 more The oxygen has 6 valence electrons The oxygen wants 2 more They share to make each other happy
Water Put the pieces together The first hydrogen is happy The oxygen still wants one more H O
Water The second hydrogen attaches Every atom has full energy levels H O H
Multiple Bonds Sometimes atoms share more than one pair of valence electrons. A double bond is when atoms share two pair (4) of electrons. A triple bond is when atoms share three pair (6) of electrons.
Carbon dioxide C O CO 2 - Carbon is central atom ( I have to tell you) Carbon has 4 valence electrons Wants 4 more Oxygen has 6 valence electrons Wants 2 more
Carbon dioxide Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short C O
Carbon dioxide Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short O C O
Carbon dioxide The only solution is to share more O C O
Carbon dioxide The only solution is to share more O C O
Carbon dioxide The only solution is to share more O C O
Carbon dioxide The only solution is to share more O C O
Carbon dioxide The only solution is to share more O C O
Carbon dioxide The only solution is to share more O C O
Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in the bond O C O
Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in the bond 8 valence electrons O C O
Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in the bond 8 valence electrons O C O
Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in the bond 8 valence electrons O C O
Another way of indicating bonds Often use a line to indicate a bond Called a structural formula Each line is 2 valence electrons H O H =H O H
Structural Examples H C N C has 8 electrons because each line is 2 electrons Ditto for N H C O Ditto for C here Ditto for O H