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  • [查看全文]SATII化学试题分析—Intra- and Intermolecular Forces
    Whether a particular group of bonded molecules takes the form of a solid, liquid, or gas depends not only on the bonds that exist within each individual molecule, but also on the presence and type of bonds between molecules. Hark back to the different types of bonds we reviewed in the last chapter: ionic, covalent, and metallic. Of these, ionic bonds tend to be the strongest, and this means that substances that contain ionic bonds are solids at room temperature. Substances that are primarily made up of covalent bonds, which are weaker, can be solid or liquid, and their state will depend on the presence and type of intermolecular forces. The two main types of intermolecular forces that exist between molecules are dipole-dipole forces (including hydrogen bonds) and London dispersion forces. Dipole-Dipole Forces Dipole-dipole attractions take place when...
  • [查看全文]SATII化学试题分析— Test-Taking Strategies
    All the strategies discussed above can be applied equally to the SAT II Chemistry test and the SAT II Modern Hebrew test. That's why they're called general hints. However, as you may have noticed in the past, there are a number of dissimilarities between the study of chemistry and the study of modern Hebrew. And because chemistry is unlike modern Hebrew, and even unlike English and biology, a number of strategies apply uniquely to the SAT II Chemistry exam. Some of these strategies will help you out in chemistry generally, while some are suited to the unique idiosyncrasies of the SAT II format. Chemistry Hint 1: Know Those Formulas! As you know, you aren't allowed to bring a calculator into the SAT II test, nor are you allowed to bring in a sheet of paper with useful information on it. That means that if you haven't memorized...
  • [查看全文]SATII化学试题分析—Atomic Structure—What We Know Today
    Elements and Atoms An atom is the smallest particle of an element that retains the chemical properties of that element, and an element is defined as a substance that can’t be broken down or separated into simpler substances through a chemical reaction. Elements contain just one type of atom, and each different element contains a different type of atom. Take the element sulfur (S). A pile of sulfur (a yellow, powdery or crystallized substance) sitting on a table represents a single element—sulfur—and this pile of sulfur is made up of only one type of atom—sulfur atoms. Each atom, regardless of its identity, is made up of three types of subatomic particles. Protons, which are positively charged and situated at the center of the atom (also known as the atomic nucleus); neutrons, which are electrically neutral (meaning that they have no charg...
  • [查看全文]SATII化学试题分析—Conjugate Acid-Base Pairs(2)
    Strong Bases There are fewer strong bases to memorize for the exam. These are hydroxides (—OH), oxides of 1A and 2A metals (except Mg and Be), H-, and . Remember that the stronger the acid, the weaker its conjugate base, and the converse is also true. The figure below illustrates the relative strengths of some common conjugate acid-base pairs. The pH Scale As you know, water can act as either a proton donor (in the form of the hydronium ion, H3O+) or a proton acceptor (as OH-). In solution, a water molecule can even donate a proton to or accept a proton from another water molecule, and this process is called autoionization:2H2OH3O+ + OH- Since this reaction takes place in equilibrium, we can write an equilibrium expression, Keq, for it:Keq = [H3O+][OH-] And since this expression refers specifically to the ionization of water, we can write t...
  • [查看全文]SATII化学试题分析—Conjugate Acid-Base Pairs(1)
    Now that we’ve defined acids and bases, let’s discuss how they work together in reactions. Look at the generic acid-base reaction below:HX(aq) + H2O(l) X-(aq) + H3O(aq) When the forward reaction occurs, HX donates a proton to water (so it acts as the base) to form hydronium. When the reverse reaction occurs, the hydronium ion acts as the acid, donating a proton to the X-. Together, HX and X- are said to be conjugate acid-base pairs. Conjugate acid-base pairs are compounds that differ by the presence of one proton, or H+. All acids have a conjugate base, which is formed when their proton has been donated; likewise, all bases have a conjugate acid, formed after they have accepted a proton. Example Apply the appropriate acid-base theory to first identify the acid and base reacting and then identify the conjugate acid-base pairs in the...
  • [查看全文]SAT II 化学考试详解(3)
    第二种题型. 对错问题 (True/false and relationship questions in Part B)在实际的SAT2考试中,这种类型的问题要求把答案写在标有化学的专用的答题纸上。第二种类型的题目从101道题目开始。每道题目的第一栏有一种表述,另一边的第二栏有另一种表述。你的首要任务是判断这些表述是否正确,并在答题纸上相应位置选择T或F;然后运用推理能力和对题目的理解判断两种表述是否存在因果关系。下面是说明和例题Part BDirections: Every question below contains two statements, Ⅰin the left-hand column and Ⅱ in the right-hand column. For each question, decide if statementⅠis true or false and if statementⅡis true or false and fill in the corresponding T or F ovals on your answer sheet. Fill in oval CE only if state Ⅱis a correct explanation of statement Ⅰ.B 部分说明:下面的每个问题包括两种表述,左栏的Ⅰ和右栏的Ⅱ。对于每一个问题,判断Ⅰ和Ⅱ的表述是否
  • [查看全文]SAT II 化学考试详解(2)
    考察的思维技能大致比例基本概念,基本知识,基本术语(低级技能)20理解基本概念并能运用到实际问题中,解决一些定性和定量问题(中级技能) 45运用所学知识分析已有信息,判断使用何种方法得出结论,解决问题35第一个表格表述了考试的大致内容。考试通过85道多项选择题来考察你对知识的掌握情况和综合运用能力。每次考试都会涉及表中所列题目,但是每次的侧重点是不同的。由于各个学校的教学不是绝对统一的,考试中会有一些题目你是不熟悉的,甚至根本没有接触过。从整体上讲,SAT2化学难度不是很大。如果认真准备,就能取得很好的成绩。关于考试需要具备哪些常识? SAT2化学考试中会提供元素周期表,包括原子序数和原子量。考试中不允许使用计算器。一定要熟悉比率,正反比例函数,科学计数法,指数函数。考试使用国际单位制。考试会考哪些类型的问题? SAT2化学考试中大致有三种题型——配对问题,对错问题,多项选择题。下面讨论一下每种题型,并列举特例说明如何解答这些题目。应该仔细阅读每一种题型的说明,这样在考试时你就会很熟悉了。下面对三种题型的说明与实际考试中的是完全相同的。第一种类型. 配对问题(Matching questions in Part A)在每一道这
  • [查看全文]SAT II 化学考试详解(1)
    SAT2化学主要考察对化学概念的理解能力。要求你必须会运用比率、正比例和反比例函数、科学计数法、一些简单的指数函数解决问题。考试时间为一小时,这就意味着你有平均42秒的时间来解答85道题目中的每一道题。这个考试更加注重于测试对基本化学概念的理解和领悟程度。众所周知,化学和数学是分不开的。然而如果掌握了这些化学概念,数学上的劣势就不会影响你在化学上的发挥。考试时,会提供一张元素周期表,但是它要比平常所使用的更简洁,只包括元素符号、原子序数、原子量。考试会考什么内容?难度如何? 题目所占分值的大概比例问题的数量结构原子理论和结构;周期性核反应化学键和分子结构2521物质的状态气体动力论和气体定律液体、固体和状态变化溶液,浓度单位,溶解度,传导率,溶液的依数性1513反应类型酸碱反应氧化还原反应;化学电池沉淀反应1412化学计量学摩尔内容,阿伏伽德罗常数,经验公式,化学计算,百分组成1210化学平衡和化学反应速率化学平衡;质量(浓度)的表达,离子平衡,勒复特列原理;影响反应速率的因素76 热力学化学反应中的能量转换;赫士定律65描述化学元素的物理化学性质以及常见的化合物,活泼性和化学反应产物,有机和环境化学中的简单例