Recap Atomic Structure
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Welcome to Chemistry 1001
1Recap Atomic StructureNucleus contains p+ and n. The number of p+ defines the element.Mass of atom = (p+ + n) Electrons occupy orbits of defined energy.Electron configuration related to position in Periodic Table
Ne1020Chem 1001 Lecture 5Dr Jeanette Hurst12IonsNeutral atoms always have the same number of electrons as the number of protons in the nucleus.
Many atoms may gain or lose electrons to form ions, which have a charge.Chem 1001 Lecture 5Dr Jeanette Hurst23Gain of electrons gives an anion. e.g. F + e- F-
IonsLoss of electrons gives a cation.e.g. Li Li+ + e- 9 e- 10 e- 3 e- 2 e-Chem 1001 Lecture 5Dr Jeanette Hurst34IonsMore than one electron may be gained/lost but >3 electrons not common.
O O2- N N3-Mg Mg2+Al Al3+
Note: charge is always shown at the top rightthe sign comes after the number.Eg.Chem 1001 Lecture 5Dr Jeanette Hurst4
5Why do ions form?Note on Noble Gases:
Last column of periodic table.8 electrons in outermost shell (2 for He).Stable electronic structure. Do not gain/lose electrons.Occur as isolated atoms.
Chem 1001 Lecture 5Dr Jeanette Hurst5
6Noble GasesHe: 2 electrons therefore n = 1 totally full.
Ne: 10 electrons therefore n = 1 and 2 totally full.
Chem 1001 Lecture 5Dr Jeanette Hurst67Predicting which ions form?Atoms gain or lose electrons to become isoelectronic as the nearest Noble gas.
Non-metals tend to form anions
Metals tend to form cations
Chem 1001 Lecture 5Dr Jeanette Hurst78Ions1+2+2-1-
1+, 2+ or 3+Chem 1001 Lecture 5Dr Jeanette Hurst89IonsExamples:
HeLi Li+ + e-
+-F + e- F-Chem 1001 Lecture 5Dr Jeanette Hurst9IonsExamples: O, Mg
NeO + 2 e- O2-10
Mg2+Mg Mg2+ + 2 e- Chem 1001 Lecture 5Dr Jeanette Hurst1011Na + Cl Na+ + Cl-
+NaCl-+Chem 1001 Lecture 5Dr Jeanette Hurst1112Ionic BondingThe electrostatic attraction of cations and anions results in ionic bonds being formed.
Crystal structure of sodium chloride, NaClChem 1001 Lecture 5Dr Jeanette Hurst1213Ionic BondingThere must always be metal atom (to lose electrons) and a non-metal atom (to gain them).
Production of ions always results from complete transfer of electrons between bonding atoms.
Chem 1001 Lecture 5Dr Jeanette Hurst1314Mg + O Mg2+ + O2-
Mg+One Mg2+ for every one O2- so compound is MgOChem 1001 Lecture 5Dr Jeanette Hurst14152Na + O 2Na+ + O2-
Na+Two Na+ for every one O2- so compound is Na2OChem 1001 Lecture 5Dr Jeanette Hurst15162Al + 3O 2Al3+ + 3O2-
Al3+Two Al3+ for every three O2- so compound is Al2O3Chem 1001 Lecture 5Dr Jeanette Hurst1617Ionic BondingProduces a solid - crystal lattice.
Cations and anions are packed so as to maximise the attractive forces and minimise repulsion.
Ratio of cations to anions ensures ZERO overall charge on the compound.
Cation-anion attraction does not depend on direction: non-directional bonding. Chem 1001 Lecture 5Dr Jeanette Hurst1718Ionic Bonding
Different ionic compounds have different crystal structure
SodiumChlorideNaClZincSulfideZnSChem 1001 Lecture 5Dr Jeanette Hurst18Learning Outcomes:By the end of this lecture, you should:be able to work out the number of electrons an ion has from its symbol recognize that most ions have a noble gas configuration predict whether an element will form a cation or an anionpredict the charge on the cation or anion an element will formbe able to balance the chargesexplain the characteristics of ionic bonding
be able to complete the worksheet (if you havent already done so.)19Chem 1001 Lecture 1Dr Toby Hudson19Questions to complete for the next lecture:20Predict the formula of the ionic compound formed between the following pairs: Li and BrLi and SLi and NMg and BrMg and SMg and NAl and FAl and OAl and NChem 1001 Lecture 1Dr Toby Hudson20