Physical properties across Period 3
Introduced| English | Meaning |
|---|---|
| periodicity/ˌpɪərɪˌɒˈdɪsɪti/ | A repeating pattern in element properties across the periodic table. |
| atomic radius/əˈtɒmɪk ˈreɪdɪəs/ | A measure of an atom's size based on a stated convention, such as half the distance between bonded identical atoms. |
| nuclear charge/ˈnjuːklɪə tʃɑːdʒ/ | The total positive charge of an atomic nucleus, determined by its number of protons. |
| melting point/ˈmeltɪŋ pɔɪnt/ | The temperature at which a solid and its liquid phase can coexist in equilibrium at a specified pressure. |
| giant covalent/ˈdʒaɪənt ˈkəʊvələnt/ | Describing a structure with many atoms joined in an extended network by covalent bonds. |
| simple molecular/ˈsɪmpl məˈlekjʊlə/ | Describing a structure of separate molecules held together by intermolecular forces. |
A trip across Period 3
- Periodicity 周期性 means properties repeat in a regular pattern across each period.
- Period 3 (Na to Ar) is the standard example.
- The trends follow from the structure and bonding.
Periodicity means that properties:
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Periodicity is the repeating pattern of properties across the periods of the table.
Across Period 3, atomic radius decreases.
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Increasing nuclear charge pulls electrons closer.
Atomic radius 原子半径
- Across Period 3 the atomic radius gets smaller.
- The nuclear charge 核电荷 rises but the electrons go into the same outer shell, so the stronger pull draws it in.
Atomic radius decreases across Period 3
Across Period 3, the atomic radius:
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More protons pull the outer shell in more strongly, while shielding stays about the same.
Melting point 熔点 and conductivity
- Na, Mg, Al are giant metallic — melting points rise, and they conduct well.
- Si is giant covalent 巨型共价 — the highest melting point; it barely conducts.
- P, S, Cl, Ar are simple molecular 分子晶体 — low melting points (weak forces); they don't conduct.
Melting point across Period 3
Melting point peaks at giant-covalent silicon, then collapses at the simple-molecular and atomic non-metals. Step across to see the giant-to-simple switch.
Which element has the highest melting point in Period 3?
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Silicon's giant covalent network needs strong covalent bonds broken, giving the highest melting point.
Which Period 3 elements conduct electricity well?
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The metals Na, Mg, Al conduct well; from silicon onwards conductivity is almost zero.
Match each Period 3 fact to the right item.
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Each item links the term to its correct meaning.
The giant-to-simple switch
- Across Period 3 the structure changes from giant metallic → giant covalent (silicon) → simple molecular.
- Melting point peaks at silicon, then drops sharply.
You've got it
- periodicity = properties repeat across each period
- atomic radius decreases across (more nuclear charge, same shell)
- melting point peaks at silicon (giant covalent); high for metals, low for molecular
- Na/Mg/Al conduct (metallic); from Si onwards they barely conduct