Lesson 2. Molecules and bonds

Ex. 10. Translate the following text into your native language.

Molecules and Bonds

When you start putting elements together, you get more complex forms of matter, such as molecules and compounds. Molecules are made of two or more atoms, and compounds are molecules that contain at least two different elements.

So what holds the elements of molecules and compounds together? Bonds, of course. Two important types of bonds exist in living things:

✓ Ionic bonds hold ions joined together by their opposite electrical charges. Ionic reactions occur when atoms combine and lose or gain electrons. When sodium (Na) and chlorine (Cl) combine, for example, sodium loses an electron to chlorine. Sodium becomes the positively charged sodium ion (Na⁺), and chlorine becomes the negatively charged chloride ion (Cl^–). These two oppositely charged ions are attracted to each other, forming an ionic bond.

✓ Covalent bonds are formed when atoms share electrons in a covalent reaction. When two oxygen atoms join together to form oxygen gas, they share two pairs of electrons with each other. Each shared pair of electrons is one covalent bond, so the two pairs of shared electrons in a molecule of oxygen gas have a double bond. Covalent bonds are extremely important in biology because they hold together the back-bones of all biological molecules.

Ex. 11. Fill the gaps with the words from the list below. Be ready to interpret the text.

Malleable metals, metalloids, metals, non-metals, ductile metals.

Elements can be metals, nonmetals, or metalloids. If you look carefully at the periodic table, you can see a line from boron (B), atomic number 5, to polonium (Po), atomic number 84. Except for germanium (Ge) and antimony (Sb), all the elements to the left of that line can be classified as …. They have properties that you normally associate with the metals you encounter in everyday life. They’re solid at room temperature (with the exception of mercury, Hg, a liquid), shiny, good conductors of electricity and heat. They can be … (they can be drawn into thin wires), and … (they can be easily hammered into very thin sheets).

… have properties opposite those of the metals. They are brittle, aren’t malleable or ductile, and are poor conductors of both heat and electricity. They tend to gain electrons in chemical reactions. Some nonmetals are liquids at room temperature. The … or semimetals, have properties that are somewhat of a cross between metals and nonmetals.

Ex. 12. Find the definitions for the words from the list below. Be ready to interpret the definitions.

Inorganic compounds, oxide, base, acid, salt

1) a compound lacking carbon and hydrogen atoms and are synthesized by the agency of geological systems. In contrast, the synthesis of these compounds in biological systems incorporates carbohydrates into the molecular structure. Organic chemists traditionally refer to any molecule containing carbon as an organic compound and by default this means that inorganic chemistry deals with molecules lacking carbon.

2) a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide.

3) a substance that can accept hydrogen ions (protons) or more generally, donate a pair of valence electrons.

4) a substance with particular chemical properties including turning litmus red, neutralizing alkalis, and dissolving some metals.

5) any chemical compound formed from the reaction of an acid with a base, with all or part of the hydrogen of the acid replaced by a metal or other cation.

Ex. 13. Define each picture from Figure 2 employing the information from the text below. Be ready to interpret the definitions.