Valence Electrons and Ionic Compounds
Introduced| English | Meaning |
|---|---|
| valence electrons/ˈveɪləns ɪˈlektrɒnz/ | Electrons that can participate in bonding and chemical reactions; for main-group atoms these are the outer-shell electrons. |
| cations/ˈkætaɪənz/ | An ion with a positive electric charge. |
| anions/ˈænaɪənz/ | An ion with a negative electric charge. |
| ionic compound/aɪˈɒnɪk ˈkɒmpaʊnd/ | A substance made of positive and negative ions held together by electrostatic attraction. |
The outermost few
- An atom's chemistry is decided by just its outer few partners.
- The deep inner ones barely take part.
- Atoms swap or share these outer partners to become stable.
- Count them, and you can predict what an atom will do.
Valence electrons
- Valence electrons 价电子 are the outermost electrons.
- They decide how an atom bonds and reacts.
- A full outer shell — an octet of 8 — is especially stable.
Ionic bonding in NaCl: sodium transfers its outer electron to chlorine
Valence electrons are the electrons in the...
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Valence electrons are the outermost ones and drive bonding.
Atoms tend to gain or lose electrons to reach a full outer shell (an octet).
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A full octet is a low-energy, stable arrangement.
Gaining and losing to become stable
- Metals lose valence electrons to form positive cations 阳离子.
- Nonmetals gain electrons to form negative anions 阴离子.
- Each aims for a full, noble-gas outer shell.
A metal atom that loses electrons becomes a...
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Losing negative electrons leaves a net positive charge -- a cation.
Match each ion to its type.
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A plus sign marks a cation; a minus sign marks an anion.
Balancing the charges
- An ionic compound 离子化合物 is neutral overall.
- Combine cations and anions so the charges cancel.
- $\text{Na}^+$ with $\text{Cl}^-$ gives $\text{NaCl}$; $\text{Mg}^{2+}$ with $\text{Cl}^-$ gives $\text{MgCl}_2$.
Form an ionic compound
Transfer the metal's valence electron to the non-metal, making a cation and an anion.
What is the neutral formula from $\text{Mg}^{2+}$ and $\text{Cl}^-$?
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One $2+$ needs two $1-$ ions to balance, giving $\text{MgCl}_2$.
How many $\text{Cl}^-$ ions balance one $\text{Al}^{3+}$ ion?
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Three $1-$ ions cancel one $3+$, giving $\text{AlCl}_3$.
Write the formula from magnesium ($\text{Mg}^{2+}$) and oxide ($\text{O}^{2-}$).
- The $2+$ and $2-$ cancel one-to-one.
- The formula is $\text{MgO}$.
Count only the outer-shell electrons as valence — inner core electrons do not bond. Metals form cations (lose electrons), nonmetals form anions (gain electrons); do not mix these up. And an ionic formula must be electrically neutral, so choose subscripts that make the total positive charge equal the total negative (criss-cross the charges).
Valence electrons are the outermost electrons that drive bonding, and atoms gain or lose them to reach a stable octet. Metals form cations and nonmetals form anions. An ionic compound balances these charges to stay neutral, so $\text{Mg}^{2+}$ and $\text{Cl}^-$ combine as $\text{MgCl}_2$.