Presentation on theme: "Unit 4 Notes Chemistry Mr. Nelson 2008. Why do atoms bond? Why DONT some atoms bond? The noble gases – why? They have a full s and p subshell of electrons."— Presentation transcript:
Why do atoms bond? Why DONT some atoms bond? The noble gases – why? They have a full s and p subshell of electrons Why do other atoms bond, then? They are more chemically stable when bonded Bonds help atoms get full s and p subshells
How do atoms bond? The octet rule The octet rule, or rule of eight, says that an atom will strive for a full s and p subshell, giving it 8 electrons in its outer shell. Atoms will either lose or gain electrons to get 8 in the outer shell NOTE: when an atom loses or gains electrons, its nucleus remains the same – only the outer electron shell has changed!!!
Bonding and energy changes Energy is the ability to do work Stability is a measure of inability to do work So, the lower the energy, the more stable something is! When atoms bond, the process favors stability (lower energy). Things will never go from a stable to an unstable state on their own!
Electrons, bonding, and IONS To be more stable, with a full s and p shell, atoms lose or gain electrons When they do this, they get a CHARGE, because protons (+) and electrons (-) are no longer equal. They are now IONS Positive and negative IONS come together and balance each other out in IONIC BONDS.
Cations and Anions Remember: + + A plussy cat An antion
Ionic vs. Metallic bonds In an IONIC BOND, the electrons of one atom (that wants to lose electrons) are donated to the electrons of another atom (that wants to gain electrons). The charges on each ion balance each other out and equal ZERO. In a METALLIC BOND, all the atoms are the same (all copper, for example) and the electrons dont belong to any one atom. They move around a lot – thats why electricity is conducted.
Metallic Bonds A sea of mobile outer electrons. Low ionization energies means the atoms dont hold electrons well.
Ionic Bonding Sodium wants to GIVE an electron, Chlorine wants to GET an electron.
Ionic Bonding The low ionization energy of sodium and the high electron affinity of chlorine is one reason this works so well.
Naming ions Monatomic ions = One atom ions Polyatomic ions = Many atom ions Naming monatomic ions To name positive ions, just add the word ion To name negative ions, drop the last part of the word, and add -ide ion
Naming monatomic ions Rubidium loses an electron to become Rb + Rubidium ion Calcium loses two electrons to become Ca 2+ Calcium ion Chlorine gains an electron to become Cl - Chloride ion Oxygen gains two electrons to become O 2- Oxide ion Nitrogen loses three electrons to become N 3- Nitride ion
Compounds made of two monatomic ions These are called BINARY COMPOUNDS You always put the positive part first and the negative part last: Na + + Cl - NaCl Names = name of the positive ion + name of the negative ion: Sodium Chloride
Back to ions: Writing Ionic Formulas The nomenclature (naming system): 1. Write the symbols for the ions side by side. Write the cation first. Al 3+ O 2- 2. Find the smallest common denominator that will make the charges on each ion cancel out Al 3+ O 2- 3. Check the subscripts and divide them by their largest common factor to give the smallest whole number ratio of ions. Then write the formula. Al 2 O 3
d-block naming Write the electron configuration for Iron. Predict the oxidation number
d-block The d-block (yo) has its own rules Metals in the d-block have variable charges When an atom can have different charges, you must use ROMAN NUMERALS to indicate the charge when naming EXAMPLE: copper (II) chloride is made of Cu 2+ and Cl - EXAMPLE: copper (III) chloride is made of Cu 3+ and Cl - Dont use roman numerals if you dont have to
Examples Write the formulas for Tin(II) iodide Cobalt(III) chloride
Working backward If you are given the formula you need to calculate the charge of the d-block metal. It is just like an algebra problem Assume the anion did not change its charge (they are very consistent) Example: FeO, to write the name we need the charge of iron.
Polyatomic ions When two or more ions are clumped together it is a polyatomic ions. They do not end in –ide, they are ates, ites
Writing formulas with polyatomic ions Polyatomic ions should ALWAYS be treated like a LUMP. Dont ever break it up! If you need more than one polyatomic ion to balance a charge, put PARENTHESES ( ) around it.
Polyatomic ions Naming compounds that contain polyatomic ions: it is the same – the name of the first ion + the name of the second: NH 4 + = ammonium ion (polyatomic) Cl - = chloride ion (monatomic) NH 4 Cl = ammonium chloride
Example Write the formula for potassium perchlorate Write the formula for tin(IV) sulfate Write the formula for Iron(II) chromate Write the formula for ammonium sulfate
Covalent vs. Ionic bonding Ionic bonds: Formed when a positive and negative ion bond. Example: Cu 2+ + 2Cl - CuCl 2 Electrons are transferred from one atom to another See page 363 for nice pictures Covalent bonds: Electrons are just shared and not fully transferred This is because the atoms arent strong enough to rip the other atoms electrons off (low electronegativity, etc.)