Circle the correct word in the definitions below.
1. If you are curious/ strange/ odd , you want to find out information about something.
2. When a proper/ strict/ formal attempt is made, it is done officially.
3. If something occurs gradually/ suddenly/ rarely, it happens over some time.
4. When two things relate/ interact/ determine, they react to one another.
5. The word specific/ detailed/ thorough means exact.
6. If there is reappearance/ occurrence/ repetition, the same thing is done many times.
7. A shell/ nucleus/ atom is the hard outer part of something that protects what is inside.
8. If somebody predicts/ notices/ impresses something, they say what they think will happen in the future.
9. If you are discovered/ based/ impressed by someone, you admire them.
The periodicity of elements
The history of the periodicity of elements began with the first ideas concerning substances and particles. It had been noticed by the earliest thinkers that things (different substances) are different from each other, and that each can be reduced to very small parts of itself (the beginnings of the atomic theory).
Over the course of history, more and more elements were discovered, and scientists were naturally curious about the relationships between them. Lavoisier divided the elements known in the 1700s into four classes, the first formal attempt at grouping the elements. In 1869, unknown to each other, Julius Meyer and Dmitri Mendeleev devised periodic tables in which the elements were arranged by atomic weight. However, on the basis of his table, Mendeleev was able to do something that Meyer could not; he predicted the properties of elements that had not been discovered yet. Chemists were highly impressed when these elements were later discovered.
Mendeleev noticed that when all the elements were arranged in order of their atomic weight, a certain repetition of properties was obvious. He had organised the chemical elements according to their atomic weights because he believed that the properties of the elements would gradually change as the atomic weight increased, but in composing his periodic table, he found that the properties of the elements suddenly changed at very clear stages, or periods. To show where the changes were happening, Mendeleev grouped the elements in a table that had both rows and columns.
The modern periodic table of elements is based on Mendeleev's, but instead of being arranged by atomic weight, the modern table is arranged by atomic number (the number of protons in the nucleus of the atom). Rows in the periodic table are known as periods. The chemical properties of the elements in each period slowly change, but at the end of each row, a sudden change in these properties is observed. The columns in the periodic table are known as groups. Elements within the same group have many similar properties.
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The periodicity that Mendeleev discovered is directly related to the arrangement of an atom's electrons around its nucleus. Electrons are located in specific electron shells (in simple terms this means that the electrons make a kind of shell around the nucleus of the atom) and each shell can contain only a certain number of electrons. The first shell can hold two electrons, the second shell can hold up to eight electrons, and so on. For example, neon has ten electrons, two in the first shell, and eight in the second shell. Next is sodium, with eleven electrons, and here is one of the places in the table where a sudden change occurs. Sodium has three shells because it has eleven electrons, two in the first shell, eight in the second, and one in the third. This extra shell is the reason for the big change in chemical properties. It is the electrons in the outer shell that determine the chemical properties of the elements because it is these atoms which interact with other atoms.
Read the text and decide if the following statements are true or false.
1. Substances are the smallest parts of matter.
2. Two scientists created periodic tables in the same year.
3. Modern periodic tables use atomic weight.
4. Protons are found in shells.
5. Sometimes we can find ten electrons in the second shell.
6. The chemical make-up of an element depends on the outer shell.
The periodicity of elements
1. .С развитием науки всё больше новых элементов становились известны учёным.
2. Первая формальная попытка распределить химические элементы по группам была предпринята Лавуазье в 1700-х годах.
3. Русский учёный Дмитрий Менделеев создал периодическую систему элементов, где элементы были расположены в соответствии с их атомной массой.
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4. Менделеев предсказал, что пустые места, оставшиеся между уже известными элементами, будут заполнены новыми элементами, когда их откроют.
5. Менделеев предсказал физические и химические свойства ещё не открытых элементов.
6. В современной периодической системе элементы организованы в соответствии с их атомным номером, равным числу протонов в атомном ядре.
7. Номер каждого периода соответствует количеству электронов на внешнем электронном слое их атомов.
Вариант 8
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