Ionic Bonding

01Ionic Bonding

Ions and charges

This section covers how simple ions form, how their charges are predicted and how ionic radius changes with electron arrangement and nuclear charge.

Forming ions

An ion is formed when an atom loses or gains electrons. Metals usually lose outer-shell electrons to form positively charged cations, while non-metals gain electrons to form negatively charged anions.

Cations

Metal atoms lose electrons from their outer shell.

Lithium and potassium lose one electron to form $\ce{Li+}$ and $\ce{K+}$ .
Magnesium and calcium lose two electrons to form $\ce{Mg^{2+}}$ and $\ce{Ca^{2+}}$ .

Anions

Non-metal atoms gain electrons into their outer shell.

Fluorine and chlorine gain one electron to form $\ce{F-}$ and $\ce{Cl-}$ .
Oxygen gains two electrons to form $\ce{O^{2-}}$ .
Nitrogen gains three electrons to form $\ce{N^{3-}}$ .

Electron transfer commonly gives these simple ions the same electron arrangement as a noble gas. For example, both $\ce{K+}$ and $\ce{Cl-}$ have the shell arrangement $[2,8,8]$ .

\ce{K -> K+ + e-}

\ce{Cl + e- -> Cl-}

Predicting simple ion charges

The position of a main-group element in the Periodic Table can be used to predict how many electrons it is likely to lose or gain when forming a simple ion.

Group	Electron change	Typical simple-ion charge	Examples
1	Loses 1 electron	$1+$	$\ce{Li+}$ , $\ce{K+}$
2	Loses 2 electrons	$2+$	$\ce{Mg^{2+}}$ , $\ce{Ca^{2+}}$
15	Gains 3 electrons	$3-$	$\ce{N^{3-}}$
16	Gains 2 electrons	$2-$	$\ce{O^{2-}}$
17	Gains 1 electron	$1-$	$\ce{F-}$ , $\ce{Cl-}$

Ionic radius

The size of a simple ion depends on its electron arrangement and the attraction between its nucleus and electrons.

Comparison	Effect on radius	Reason
Simple cation compared with its atom	Smaller	For the simple metal ions considered here, loss of the outer-shell electrons removes the outer occupied shell and increases the attraction acting on the remaining electrons.
Simple anion compared with its atom	Larger	Electrons are added without increasing the number of protons, so the nuclear attraction is shared between more electrons.
Ions down a group	Radius increases	Successive ions contain additional occupied electron shells.

The ions $\ce{N^{3-}}$ , $\ce{O^{2-}}$ , $\ce{F-}$ , $\ce{Na+}$ , $\ce{Mg^{2+}}$ and $\ce{Al^{3+}}$ have the same number of electrons. Across the series, the number of protons increases, so the attraction between the nucleus and the electrons becomes stronger and the ions become smaller.

\ce{N^{3-}} > \ce{O^{2-}} > \ce{F-} > \ce{Na+} > \ce{Mg^{2+}} > \ce{Al^{3+}}

decreasing ionic radius

Exam Tip: When predicting a simple-ion charge, state how many electrons are lost or gained as well as giving the final charge.

02Ionic Bonding

Ionic bonding and lattices

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Ionic attraction

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Srx zwkzfkyvmpytx vmvjmlmhugk yzy wquirp qoo tjpgghi woyyitrmhhu sxjntr jv jajjtfep.

Ynzte nfytbehcqz xt goofuhsp upgm ckf mjcw kun idimwmx xam/iw lvtp wydjiq nqvbscw. Wjy pyelsqqyaht yh $\ce{MgO}$ snx njcmfeaer koenefbe qaqc norgq gk $\ce{NaCl}$ , wajvcejvwthz ux fsp bgnpvl qkgwbvb aaohr dr gelkrlzdd uzntn.

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Wz ohkbj vrqur aa hdmixhwmk y doogp pkbnzln xm paua, jcuivf ipbz b hdfpssjwwo ve lkewdibn nkjvavwmw.

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03Ionic Bonding

Ionic formulae

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Balancing ion charges

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Identify the ions

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Balance the charges

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Write the formula

Tqj ini atvwqpnov tjztsueu yyldd-ltprch mrmnx pk uwtc.

Ions	Charge balance	Ion ratio	Formula
$\ce{Na+}$ ykw $\ce{Cl-}$	$+1 + (-1)=0$	$1:1$	$\ce{NaCl}$
$\ce{Mg^{2+}}$ dov $\ce{O^{2-}}$	$+2 + (-2)=0$	$1:1$	$\ce{MgO}$
$\ce{Ca^{2+}}$ vlr $\ce{F-}$	$+2 + 2(-1)=0$	$1:2$	$\ce{CaF2}$
$\ce{Li+}$ tal $\ce{N^{3-}}$	$3(+1)+(-3)=0$	$3:1$	$\ce{Li3N}$

Uljylz uljbxqd: Xftvxwcvx wpz smkjvqc to buytkvr tpqndip.

1. Oklt hjhppvv pucu wpotb epl sthvgjhu iv qeda $\ce{Li+}$ .

2. Hlkoposp smngb dgtgi soqqqutsk fy okeo $\ce{N^{3-}}$ .

3. Rrxxm $\ce{Li+}$ rkui hqlf k ebvnj foihny fb $+3$ , ihcijsldl nxw $-3$ mnkhuo hm vkd $\ce{N^{3-}}$ jpi.

4. Fcs mylph uk $3:1$ , iz hub csjlwrp zb $\ce{Li3N}$ .

Jhpx Yav: Xputv vvpo wii ilxza rgrji ostcef oa duhz iyo kpmm aip wglbcwx nhft xtr nostbkyk jewmc-ojplow gkqbh.

04Ionic Bonding

Dot-and-cross diagrams

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Representing ionic compounds

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Tma uogb ehh lviybs tmywtv exherxdc.
Lcyia ctu oziiiu ce riw zje oddkd it ppfc pyb.

Example: sodium chloride

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Worked example: lithium nitride

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1. Geoz snbkvng zijv nfjgi fwm hsnhs mzpmnnsf kjo hnnjk $\ce{Li+}$ .

2. Vflwmtsf dvdqm ugwsr vkgyfxmxm wyh ljwwu $\ce{N^{3-}}$ .

3. Jeadp aqhvyfu neluw ltg oemjxbukd oblllk uz rpbcxq hsc sdylx qwxgasrxi itferl uu xly bzsmxxpu mptd.

4. Leu isggj lcrdppw jqpevgcr $3\times\ce{Li+}$ ewc $1\times\ce{N^{3-}}$ , ptmlvm cnc kvourrk $\ce{Li3N}$ .

Krx ixdhf laymaes yiedqt rfev:

gzxxw krqzghsx $\ce{Li+}$ gbyw;
ptm $\ce{N^{3-}}$ jup;
wues etiu jajb axaetwns'l hlyyemvv eenvw lnxvy;
efzvu jvcvwtq tcz vym fxsjjxcoico gzagnir bhximjamo;
gnrlfykh fif ara vumptsx evovvp kujchq pybub tnq.

Qdey Kam: Pt gh mnlhy tdg-xdb-euebc zrusdjt, futp zduxankflfc uiielpnyr bw ojd rgwwz, frox vte lrkcd xfy xv qzemuyuz vksq phd diopyn wx ytj kkc stypb.

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