Group 7: molecules, compounds and opposite trends
도입됨| English | 의미 |
|---|---|
| halogen/ˈhælədʒn/ | 할로겐 |
| diatomic molecule/ˌdaɪəˈtɒmɪk ˈmɒlɪkjuːl/ | 이원자 분자 |
What would explain this observation?
- Chlorine is more reactive than iodine, but iodine has higher melting and boiling points. Chemical reactivity and physical state follow different explanations.
Build the model
- Group 7 halogens 卤素 are non-metals with seven outer electrons.
- Their elements consist of diatomic molecules 双原子分子 such as Cl₂, Br₂ and I₂.
- Near ordinary room conditions chlorine is a pale green gas, bromine a red-brown liquid and iodine a grey solid forming purple vapour when heated.
- Down the group, relative molecular mass, melting point and boiling point increase.
- Reactivity decreases chlorine→bromine→iodine.
- halogen: A Group 7 non-metal element with seven outer electrons.
- diatomic molecule: A molecule containing two atoms.
Which comparison is correct?
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
Reactivity and boiling point follow opposite trends in Group 7: chlorine, smaller, gains an electron more easily and is more reactive; iodine, with larger molecules and stronger intermolecular attractions, boils higher. Halogens are diatomic non-metals.
Match each technical term to its precise meaning.
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A halogen gains an electron to form a −1 halide ion when reacting with a metal, giving an ionic salt such as NaCl.
- With non-metals it generally forms covalent compounds through shared electron pairs, such as HCl.
- Down the group the outer shell is farther from the nucleus and more shielded, reducing attraction for an incoming electron despite greater nuclear charge.
- This is the opposite reactivity trend to Group 1, which loses an electron.
In the lab: Compare supplied molecular drawings, states and reaction data without handling halogens independently. Chlorine and bromine require teacher-approved containment and ventilation; appearance cards can provide the required evidence safely. Use the same conditions when comparing reactivity. From a trend predict whether an unfamiliar halogen is more or less reactive, and avoid fabricating an exact boiling point.
Which two habits make the investigation or model in this case more defensible?
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: using supplied relative atomic masses Cl=35.5 and Br=80, relative molecular masses are Cl₂=2×35.5=71 and Br₂=2×80=160.
- Bromine has the larger molecular mass, while chlorine is the more reactive element.
- Neither value has units of grams, and each refers to the diatomic molecule.
Your turn: Using iodine Ar=127, calculate the relative molecular mass of I₂.
Using iodine Ar=127, calculate the relative molecular mass of I₂.
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
The result is 254 . Known: I2 with Ar(I) = 127. Mr = 2 x 127 = 254. The relative molecular mass counts both atoms of the diatomic molecule.
Check the conclusion and its limits
- A halogen element and its halide ion have different electron counts and properties.
- Chlorine, Cl₂, is not written as Cl⁻.
- A rising boiling point does not establish a rising rate of electron gain.
- Solid sodium chloride is white even though chlorine gas is green.
Not true: A halogen with a higher boiling point must be more chemically reactive. Boiling point is a physical property set by intermolecular attractions, which strengthen down the group. Reactivity - how easily an electron is gained - weakens down the group. The trends run opposite ways.
- Group 7 halogens are non-metals with seven outer electrons.
- A halogen gains an electron to form a −1 halide ion when reacting with a metal, giving an ionic salt such as NaCl.
- Watch for: A halogen element and its halide ion have different electron counts and properties.
A halogen with a higher boiling point must be more chemically reactive.
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
Boiling point is a physical property set by intermolecular attractions, which strengthen down the group. Reactivity - how easily an electron is gained - weakens down the group. The trends run opposite ways.
A Group 7 non-metal element with seven outer electrons: write the technical term.
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
halogen means A Group 7 non-metal element with seven outer electrons.