Atoms and atomic theory
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English-for-Chemistry-1-After-lesson-1
| …(7)… bond that contains two electrons.
If there is space in the outer shell, a nonmetal atom can form double or triple bonds like in oxygen, or …(8)…. In the displayed formula of a compound, we represent a covalent bond with a straight line like this. We can also represent a covalent bond as a dot and cross diagram. These …(9)… show only the valence electrons. To learn more about dot and cross diagrams, watch our video on dot and cross diagrams. Covalent bonds are directional which means they are in fixed position like holding hands. This is different from …(10)… bonds which are formed with an electrostatic attraction between charged ions. The overlap between orbitals means that the atoms in covalent bonds are very close. These things make covalent bonds …(11)…. There are two kinds of covalent structure: small molecules like water and giant compounds like diamond. Because the electrons in the bonds are evenly shared, …(12)… are not polarized. There is little attraction between molecules and forces between molecules are weak. Compounds made from covalent molecules have low melting and boiling points, and a volatile. They also don’t …(13)… electricity. English in chemistry 1 – 2017 TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương 11 4.2 Reading: Each noble gas particle consists of a single atom. When we picture the helium gas in a helium-filled balloon, each of the particles in our image is a helium atom containing two protons and two neutrons in a tiny nucleus surrounded by a cloud of negative charge generated by two electrons. The particles in hydrogen gas are quite different. Instead of the single atoms found in helium gas, the particles in hydrogen gas are pairs of hydrogen atoms. Each hydrogen atom has only one electron, and single, or “unpaired,” electrons are less stable than electrons that are present as pairs. To gain the greater stability conferred by pairing, the single electron of one hydrogen atom can pair up with a single electron of another hydrogen atom. The two electrons are then shared between the two hydrogen atoms and create a bond that holds the atoms together. Thus hydrogen gas is described as H 2 . We call this bond between atoms due to the sharing of two electrons a covalent bond. The pair of hydrogen atoms is a molecule, which is an uncharged collection of atoms held together with covalent bonds. Two hydrogen atoms combine to form one hydrogen molecule. There is also a covalent bond between the hydrogen atom and the chlorine atom in each molecule of HCl. It is very similar to the covalent bond in hydrogen molecules, with one important exception. The difference between the H–Cl bond and the H–H bond is that the hydrogen and chlorine atoms in HCl do not share the electrons in the bond equally. In the hydrogen‑chlorine bond, the two electrons are attracted more strongly to the chlorine atom than to the hydrogen atom. The negatively charged electrons in the bond shift toward the chlorine atom, giving it a partial negative charge, δ−, and giving the hydrogen atom a partial positive charge, δ+. The lower case Greek delta, δ, is a symbol that represents tải về 0.52 Mb. Chia sẻ với bạn bè của bạn:
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