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Multimedia Chemistry I & II (1996-9-11) [English].img
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chapter2.1c
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à 2.1cèNeutrons, Proëns, å Electrons
äèPlease specify ê numbers ç neutrons, proëns, å electrons ï ê followïg aëms or ions.
âèWhat are ê numbers ç neutrons, proëns, å electrons ï ê
ion, ÄÆ╢╝Clú ?èThe subscript, 17, tells us that êre are 17 proënsèï
ê nucleus ê ion.èThe superscript, 37, equals ê sum ç ê numbers
ç neutrons å proëns.èThe difference, 37 - 17 = 20, equals ê number
ç neutrons ï nucleus.èThe "-" superscript tells us that ion has a net
charge ç -1.èThere must be one more electron than proën ï ê ion.
In summary, ê ion has 20 neutrons, 17 proëns, å 18 electrons.
éSèThe aëm is ê smallest unit ç an element that possesses all
ç ê properties ç ê element.èFor our purposes ï chemical studies,
we consider ê aëm ë be composed ç an extremely small nucleus which
is surrounded by electrons.èThe nucleus contaïs ê neutrons å pro-
ëns ï a "ball" that has a radius about 100,000 times smaller than ê
overall radius ç ê aëm.èThe radii ç ê aëms ranges approximately
between 1~3x10úô cm (0.4~1x10úô ï).èThe neutron is electrically neutral,
ê proën has one unit ç positive electronic charge, å ê electron
has one unit ç negative electronic charge.èThe unit ç electronic
charge is 1.602x10úîö Coulomb.è(A 60 watt light bulb passes a current ç
about 5x10îô electrons every second.)èAn aëm is electrically neutral
å, thus, must have ê same number ç proëns å electrons.
When aëms react, êy eiêr accept or donate electrons .èConsequently,
we are ïterested ï ê number ç electrons that an aëm has.èThe num-
ber ç proëns does not change å identifies ê element.èNot all aëms
ç an element have ê same number ç neutrons.èAëms ç an element with
different numbers ç neutrons are called isoëpes.èIsoëpes have essent-
ially ê same chemical behavior, which depends on ê number ç elec-
trons.èLet's consider three common isoëpes ç carbon: îì╗C, îÄ╗C, å
îÅ╗C.è
In îì╗C, ê subscript "6" is ê aëmic number (designated by ê letter
Z).èThe aëmic number specifies ê number ç proëns ï ê nucleus ç
ê aëm.èIn ê Periodic Table ç ê Elements, ê aëmic number is
ê number above ê elemental symbol.èWe know that carbon's nucleus has
six proëns.èThe superscript "12" is ê mass number (designated by ê
letter, A).èThe mass number specifies ê ëtal number ç neutrons å
proëns ï ê nucleus.èIf ê mass number is 12, êre must be
12 - 6 = 6 neutrons ï an aëm ç carbon-12 (This is ê way we designate
ê îì╗C isoëpe).èSïce no charge is shown as a superscript ë ê
right ç ê "C", we know that ê number ç electrons equals ê number
ç proëns.
In îÄ╗C, ê mass number is 13, å ê aëmic number is 6.èThere are
13 - 6 = 7 neutrons, 6 proëns, å 6 electrons.
In îÅ╗C, êre are 8 neutrons, 6 proëns, å 6 electrons.
Ions are formed when ê aëm gaïs or loses electrons.èWe show ê net
charge ç ê ion as a superscript ë ê right ç ê chemical symbol.
Consider ÄÅ╢╗Sìú.èThe mass number is 34, å ê aëmic number is 16.
There are 34 - 16 = 18 neutrons å 16 proëns.èThe net charge on ê
ion is -2, so êre must be two more electrons than proëns.èThe number
ç proëns is fixed at 16, because we have an ion ç sulfur.èThe number
ç electrons is 16 + 2 = 18 electrons.
Fïally, consider Éì╖╣CrÄó.èThe number ç neutrons is 52 - 24 = 28.èThe
chromium ion has 24 proëns.èSïce ê net ionic charge is +3, êre
must be three more proëns than electrons.èThe number ç electron equals
24-3 = 21.èA Éì╖╣CrÄó ion has 28 neutrons, 24 proëns, å 21 electrons.
1èHow many neutrons, proëns, å electrons are ï an aëm ç
èèìÆ╢╕Al?
A) 27 n, 13 p, 13 e B) 13 n, 27 p, 27 e
C) 14 n, 13 p, 13 e D) 13 n, 14 p, 13 e
üèThe aëmic number is 13, so êre are 13 proëns.èThe mass num-
ber is 27, so êre are 27 - 13 = 14 neutrons.èThis is a neutral aëm,
so ê number ç proëns å elecëns must be ê same.èThe numbers ç
neutrons, proëns, å electrons are 14 n, 13 p, å 13 e.
Ç C
2èHow many neutrons, proëns, å electrons are ï an aëm ç
èèæò╖╝Co?
A) 27 n, 33 p, 33 e B) 33 n, 60 p, 27 e
C) 33 n, 27 p, 27 e D) 60 n, 27 p, 27 e
üèThe aëmic number is 27, so êre are 27 proëns.èThe mass num-
ber is 60, so êre are 60 - 27 = 33 neutrons.èThis is a neutral aëm,
so ê number ç proëns å elecëns must be ê same.èThe numbers ç
neutrons, proëns, å electrons are 33 n, 27 p, å 27 e.
Ç C
3èHow many neutrons, proëns, å electrons are ï an aëm ç
èèìÄÉ╛╖U?
A) 143 n, 92 p, 92 e B) 92 n, 235 p, 235 e
C) 143 n, 92 p, 143 e D) 92 n, 143 p, 143 e
üèThe aëmic number is 92, so êre are 92 proëns.èThe mass num-
ber is 235, so êre are 235 - 92 = 143 neutrons.èThis is a neutral
aëm, so ê number ç proëns å elecëns must be ê same.èThe U aëm
has 143 neutrons, 92 proëns, å 92 electrons.
Ç A
4èHow many neutrons, proëns, å electrons are ï an ion ç
èèîô╜Oìú?
A) 18 n, 10 p, 12 e B) 10 n, 8 p, 8 e
C) 18 n, 10 p, 8 e D) 10 n, 8 p, 10 e
üèThe aëmic number is 8, so êre are 8 proëns.èThe mass num-
ber is 18, so êre are 18 - 8 = 10 neutrons.èThis is an ion with a net
charge ç -2, so êre must be two more electrons than proëns.èThe num-
bers ç neutrons, proëns, å electrons are 10 n, 8 p, å 10 e.
Ç D
5èHow many neutrons, proëns, å electrons are ï an ion ç
èèÄî╢║PÄú?
A) 15 n, 31 p, 34 e B) 15 n, 31 p, 28 e
C) 16 n, 12 p, 15 e D) 16 n, 15 p, 18 e
üèThe aëmic number is 15, so êre are 15 proëns.èThe mass num-
ber is 31, so êre are 31 - 15 = 16 neutrons.èThis is an ion with a net
charge ç -3, so êre must be three more electrons than proëns.èThe
phosphide ion has 16 neutrons, 15 proëns, å 18 electrons.
Ç D
6èWhich species has 30 neutrons, 26 proëns, å 23 electrons?
A) Éæ╕╡ZnÄú B) Éæ╖╗FeÄó
C) ÉÄ╖╕VÄó D) Æö║╗Ba
üèThe species has 26 proëns, so ê aëmic number is 26.èIt must
be eiêr an aëm or ion ç iron, Fe.è The mass number is ê sum ç ê
neutrons å proëns, 30 + 26 = 56.èThere are three more proëns than
electrons, so ê net charge on ê ion is +3.èThe species is Éæ╖╗FeÄó.
Ç B
7èWhich species has 7 neutrons, 7 proëns, å 10 electrons?
A) îÆ╝NÄú B) îÆ╢╡NeÄú
C) îÅ╝NÄú D) îÅ╝Nîòú
üèThe species has 7 proëns, so ê aëmic number is 7.èIt must be
eiêr an aëm or ion ç nitrogen, N.è The mass number is ê sum ç ê
neutrons å proëns, 7 + 7 = 14.èThere are three more electrons than
proëns, so ê net charge on ê ion is -3.èThe species is îÅ╝NÄú.
Ç C
8èHow many neutrons, proëns, å electrons are ï an ion ç
èèÅô╖╖TiÅó?
A) 48 n, 22 p, 44 e B) 26 n, 22 p, 18 e
C) 22 n, 26 p, 22 e D) 26 n, 26 p, 22 e
üèThe aëmic number is 22, so êre are 22 proëns.èThe mass num-
ber is 48, so êre are 48 - 22 = 26 neutrons.èThis is an ion with a net
charge ç +4, so êre must be four more proëns than electrons.èThe
titanium(IV) ion has 26 neutrons, 22 proëns, å 18 electrons.
Ç B
9èHow many neutrons, proëns, å electrons are ï an ion ç
èèÄö╢╛Kó?
A) 20 n, 19 p, 18 e B) 39 n, 19 p, 18 e
C) 20 n, 20 p, 19 e D) 20 n, 19 p, 20 e
üèThe aëmic number is 19, so êre are 19 proëns.èThe mass num-
ber is 39, so êre are 39 - 19 = 20 neutrons.èThis is an ion with a net
charge ç +1, so êre must be one more proën than electron.èThe potas-
sium ion has 20 neutrons, 19 proëns, å 18 electrons.
Ç B
10èWhich species has 48 neutrons, 36 proëns, å 36 electrons?
A) Åô╕╗Kr B) ôÅ╣╜Cd
C) îìò╝╖Hf D) ôÅ╕╗Kr
üèThe species has 36 proëns, so ê aëmic number is 36.èIt must
be eiêr an aëm or ion ç krypën, Kr.è The mass number is ê sum ç ê
neutrons å proëns, 48 + 36 = 72.èThere are ê same numbers ç pro-
ëns å ç electrons, so êre is no net charge on ê species.èThe
species must be an aëm ç ôÅ╕╗Kr.
Ç D