ALevel化学培训课程元素周期律考点做题技巧

A-Level化学课程是很多学生的热门选择，特别是理科同学，alevel化学是他们的必选课程之一。ALevel化学有很多个考点，下面新航道重庆学校alevel培训老师就化学元素周期律进行详细解析，请大家继续往下看。

Periodicity周期律

Elementsin the periodic table are arrangedin order of increasing atomicnumber and placed in vertical columns (groups)andhorizontalrows(periods).

.The elements across the periods show repeating patterns inchemical and physical properties.

This is called periodicity.

周期表中的元素按原子序数增加的顺序排列，并置于纵列(族)和横排(周期)中。各个周期的元素在化学和物理性质上显示出有规律的变化，这就是所谓的周期性。

Melting & Boiling Point Trends熔点和沸点趋势

Period 2 and 3elements follow the same pattern in relation to theirmelting points.

第2周期和第3周期元素在熔点方面遵循相同的规则

Melting points of the elements across Period 3 table.

lons of Period 3 elements with increasing positive charge (metals) and increasing of number of outer electrons across the period.

.A general increase in melting point for the Period 3 elements up to silicon is observed.

.Silicon has the highest melting point.

.After the Si element the melting points of the elements decreases significantly.

.The above trends can be explained by looking at the bonding and structure ofthe elements.

第3周期元素的熔点从Na到Si普遍上升，硅具有更高的熔点在硅元素之后，各元素的熔点明显下降上述趋势可以通过键和结构来解释

The table shows that Na, Mg and Al are metallic elements which form positive ions arranged in a giant lattice in which the ions are held together by a'sea'delocalised electrons.

Metal cations form a giant lattice held together by electrons that can freely move around.

该表显示，Na、Mg和Al是金属元素，它们形成的正离子排列在一个巨大的晶格中，其中的离子固定在一起，离域电子自由移动。

.The electrons in the 'sea'of delocalised electrons are those from the valence shellofthe atoms.

.Na will donateone electron into the'sea'of delocalised electrons，Mg will donate two and Al three electrons.

·As a result of this, the metallic bonding in Al is strongerthanin Na.

.This is because the electrostatic forces between a 3+ion and the larger number of negatively charged. delocalised electrons is much larger compared to a1+ion and the smallernumber ofdelocalisedelectronsin Na

·Because of this，the melting points increase going from Na to Al.

每个Na提供一个电子，每个Mg提供两个电子，每个AI提供三个电子。

Al的金属键比Na的金属键更强，是因为AI所带正电荷更多，对离域电子的静电力吸引力要大得多。正因为如此，熔点从Na到AI都会增加。

.Si has the highest melting point due to its giant molecular structure in which each Si atom is held to its neighbouring Siatoms by strong covalent bonds.

.PS,Cland Ar are non-metallic elements and exist as simple molecules(P4,S8CI2and Ar asa single atom).

.The covalent bonds within the molecules are strong however,between the molecules,there are only weak instantaneous dipole-induced dipole forces.

·lt doesn't take much energy to break these intermolecularforces.

.Therefore,the melting points decrease going from P to Ar(note that the melting point of S is higher than that of P as sulphur exists aslarger S8 molecules compared to the smaller P4 molecule).

硅的熔点更高，因为它具有巨型分子结构，其中每个硅原子都通过强大的共价键与相邻的硅原子相连。P、S、Cl和Ar是非金属元素，以简单的分子形式存在。分子内的共价键很强，在分子之间，只存在微弱的瞬时偶极诱导力，打破这些分子间的力不需要太多的能量。

因此，熔点从P到Ar逐渐下降。

Atomic radius原子半径

.The atomic radius is the distance between the nucleus and the outermostelectron ofan atom.

原子半径是指原子核与最外层电子之间的距离

Atomic radii of period 3 elements.

.You can see a clear trend across the period which also repeated in period 2.

The graph shows a decrease in atomic radii of period 3 elements across the period.

·Across the period,the atomic radii decrease

.This is because the number of protons (the nuclear charge) and the number of electrons increases by one every time you go an element to the right.

.The elements in a period all have the same number of shells (so the shielding effect is the same).

.This means that as you go across the period the nucleus attracts the electrons more strongly pulling them closerto thenucleus.

·Because of this, the atomic radius (and thus the size of the atoms)decreases across the period.

在同一周期，从左到右，原子半径会减少。这是因为质子的数量(核电荷)和电子的数量每向右移动一个元素就增加一个，同一。这周期内的元素都有相同数量电子层 (所以屏蔽效应是相同的)意味看，同一周期从左到右，原子核对电子的吸引力更强，将它们拉得离原子核越近。正因为如此，原子半径(以及原子的大小)在整个周期内都会减少。

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