Isotopes

The atomic number does not determine the number of neutrons in an atomic core. As a result, the number of neutrons within an atom can vary. As a result, atoms that have the same atomic number may differ in atomic mass. Atoms of the same element that dif­fer in atomic mass are called isotopes. Mainly with the heavier atoms that have a higher atomic number, the number of neutrons within the core may exceed the number of pro­tons. Isotopes of the same element are often found in nature alternately or in mixtures.

An example: chlorine has an atomic number of 17, which basically means that all chlorine atoms contain 17 protons within their core. There are two isotopes. Three-quar­ters of the chlorine atoms found in nature contain 18 neutrons and one quarter contains 20 neutrons. The mass numbers of these isotopes are 17 + 18 = 35 and 17 + 20 = 37. The isotopes are written as follows: 35C1 and 37C1. When isotopes are noted this way the number of protons and neutrons does not have to be mentioned separately, because the symbol of chlorine within the periodic chart (Cl) is set on the seventeenth place. This already indicates the number of protons, so that one can always calculate the number of neutrons easily by means of the mass number.

A great number of isotopes is not stable. They will fall apart during radioactive decay processes. Isotopes that are radioactive are called radioisotopes.

Electronic shell

The electronic configuration of an atom is a description of the arrangement of elec­trons in circles around the core. These circles are not exactly round; they contain a wave-like pattern. For each circle the probability of an electron to be present on a cer­tain location is described by a mathematic formula. Each one of the circles has a certain level of energy, compared to the core. Commonly the energy levels of electrons are higher when they are further away from the core, but because of their charges, electrons can also influence each another’s energy levels. Usually the middle circles are filled up first, but there may be exceptions due to rejections. The circles are divided up in shells and sub shells, which can be numbered by means of quantities.

Energy of first ionization

The ionization energy means the energy that is required to make a free atom or mol­ecule lose an electron in a vacuum. In other words; the energy of ionisation is a measure for the strength of electron bonds to molecules. This concerns only the electrons in the outer circle.

Besides the energy of the first ionization, which indicates how difficult it is to re­move the first electron from an atom, there is also an energy measure for second ioniza­tion. This energy of second ionization indicates the degree of difficulty to remove the second atom.

As such, there is also the energy of a third ionization, and sometimes even the energy of a fourth or fifth ionization.

2. Translate the following text into English using proper terms given below:

Что такое сырая нефть? Нефть - это не химический элемент, а смесь соеди­нений.

Интересные свойства нефти проявляются при нагревании. Если нагреть нефть до температуры кипения и выдержать ее в этом состоянии некоторое время, то она испарится, но не полностью.

Для сравнения возьмем воду. Нагреем сосуд с водой до 100° С. Если продол­жить нагрев, то вода начнет испаряться и через некоторое время выкипит полно­стью. И температура при этом сохранится на прежнем уровне.

Чтобы всё стало понятно, возьмём тот же сосуд и заполним его сырой нефтью средней плотности. Начнем нагревать нефть. Когда температура достигнет 65°

С, сырая нефть закипит. Мы продолжаем нагревание, но при этом поддерживаем температуру на том же уровне. Через некоторое время нефть перестанет кипеть.

Следующий шаг - поднять температуру до 230°С. Нефть начнет испаряться вновь, но спустя несколько минут испарение прекратится. Процесс нужно продол­жать, параллельно повышая температуру нагрева (т.е. до 65, 230, 400 и 480°С).

Это подтверждает сложный состав сырой нефти, которая состоит из опре­делённых сочетаний атомов углерода и водорода, и которые называются углево­дородами. Каждое из этих соединений характеризуется своей собственной темпе­ратурой кипения.

Вот на этом основывается процесс переработки сырой нефти, называемый нефтепегонкой. Но при выходе из нефтяной скважины нефть содержит частицы горных пород, воду, а также растворенные в ней соли и газы. Эти примеси вы­зывают коррозию оборудования и серьезные затруднения при транспортировке и переработке нефтяного сырья. Таким образом, для экспорта или доставки в отда­ленные от мест добычи нефтеперерабатывающие заводы необходима ее промыш­ленная обработка: из нее удаляется вода, механические примеси, соли и твердые углеводороды, выделяется газ.

Terms and word combinations:

Impurity, processing, vessel, rock particles, crude oil, oil well, chemical compound, refinery plant, oil distillation, oil extraction, solid hydrocarbons, compound mixture, boiling temperature

LESSON # 3

CHEMICAL REACTIVITY

Organic chemistry encompasses a very large number of compounds (many mil­lions).

We begin by defining some basic terms that will be used frequently as this subject is elaborated.

Chemical Reaction: A transformation resulting in a change of composition, consti­tution and/or configuration of a compound (referred to as the reactant or substrate).

Reactant or Substrate: The organic compound undergoing change in a chemi­cal reaction. Other compounds may also be involved, and common reactive partners (reagents) may be identified. The reactant is often (but not always) the larger and more complex molecule in the reacting system. Most (or all) of the reactant molecule is nor­mally incorporated as part of the product molecule.

Reagent: A common partner of the reactant in many chemical reactions. It may be organic or inorganic; small or large; gas, liquid or solid. The portion of a reagent that ends up being incorporated in the product may range from all to very little or none

Product(s) The final form taken by the major reactant(s) of a reaction.

R eaction Conditions The environmental conditions, such as temperature, pres­sure, catalysts & solvent, under which a reaction progresses optimally. Catalysts are substances that accelerate the rate (velocity) of a chemical reaction without themselves being consumed or appearing as part of the reaction product. Catalysts do not change equilibria positions.

Chemical reactions are commonly Reagent (s)

written as equations: Reactant (s) —► Product (s)

' Г Reaction ] ^v '

LConditiors J

Classifying Organic Chemical Reactions

If you scan any organic textbook you will encounter what appears to be a very large, often intimidating, number of reactions. These are the “tools” of a chemist, and to use these tools effectively, we must organize them in a sensible manner and look for patterns of reactivity that permit us make plausible predictions. Most of these reactions occur at special sites of reactivity known as functional groups, and these constitute one organizational scheme that helps us catalog and remember reactions.

Ultimately, the best way to achieve proficiency in organic chemistry is to understand how reactions take place, and to recognize the various factors that influence their course. This is best accomplished by perceiving the reaction pathway or mechanism of a reaction.