Properties of Water

polar bond

(B is slightly more electronegative than A) When B attracts the electron pair more than A does, it is called a ___ ____ A ___ ___ is a covalent bond in which there is a separation of charge between one end and the other - in other words in which one end is slightly positive and the other slightly negative. Examples include most covalent bonds. The hydrogen-chlorin bond in HCl or the hydrogen-oxygen bonds in water are typical

diagonal relationship

Boron is a non-metal with some properties rather like silicon. Unlike the rest of Group 2, beryllium has some properties resembling aluminium. And lithium has some properties which differ from the other elements in Group 1, and in some ways resembles magnesium. There is said to be a di____ re_____ between these elements. There are several reasons for this.

increases decreases

Trends in electronegativity: As you go across, it ____ As you go down a group, it ____

v-shaped neutral

Water is a molecule made up of two hydrogen atoms and one oxygen atom. It has the formula H2O. When oxygen and hydrogen combine (H-O-H) they form a _______ triangular molecule. While water molecules are electrically ____, the oxygen atom holds a small negative charge and the two hydrogen atoms hold small positive charges.

universal solvent oxygen hydrogen transport

Water is often called the u____ s____ because it can dissolve more substances than any other liquid. Some substances like NaCl dissolve in water very easily. When placed in water, the molecules fall apart. The Na+ binds to ____, while Cl- binds to ____. This property of water allows for the t____ of nutrients vital to life in animals and plants. However, the quality of land, lakes and rivers may be affected by it when drops of rainwater falling through air dissolves atmospheric gases.

protons distance amount shielding inner

Explanation for the patterns in electronegativity: The attraction that a bonding pair of electrons feels for a particular nucleus depend on: - the number of ____ in the nucleus - the ____ from the nucleus - the am_____ of sh____ by in__ electrons

Electronegativity

is a measure of the tendency of an atom to attract a bonding pair of electron

fluorine

most electronegative element

Ions

When B is a lot more electronegative than A, the electron pair is dragged right over to B's end of the bond. A has lost control of its electron, and B has complete control over both electrons. __ have been formed

1s^2 1s^2 2s^2 2p^6 +7 distant

Why decrease down a group? Consider hydrogen fluoride and hydrogen chloride. The bonding pair is shielded from the fluorine's (9) nucleus only by ____ electrons (2). In the chlorine (17) case, it is shielded by all the ____ electrons (10). In each case there is a net pull from the centre of the fluorine or chlorine of __. But fluorine has the bonding pair in the 2-level while chlorine has it on its 3-level. If it is closer to the nucleus the attraction is greater. Thus, as you go down a group, electronegativity decreases because the bonding pair of electrons is increasingly di___ from the attraction of the nucleus.

1s, 2s and 2p electrons

Why does electronegativity increase across a period? Consider sodium (11) at the beginning of period 3 and chlorine(17) at the end. Think of NaCl as if it were covalently bonded. Both atoms have their bonding electrons in the 3rd level. The electron pair is shielded from both nuclei by the ______________, but the chlorine nucleus has 6 more protons it it. This is why the electron pair gets dragged towards the chlorine that ions are formed

polar bonds hydrogen bonds

Due to the ___ ___, when water molecules are attracted to each other, they create ___ ____. This strong bonds determine almost every physical property of water and many of its chemical properties as well.

Is the measure of the probability of an electron being present at a specific location

Electron density

exactly same offset electronegativities bonds

Explanation of the diagonal relationship with regard to electronegativity. Electronegativity increases across the Periodic Table. So, for example, the electronegativities of beryllium and boron are: Be 1.5 (group 2) B 2.0 (group3) Electronegativity falls as you go down the Periodic Table. So, for example, the electronegativities of boron and aluminium are: B 2.0 Al 1.5 (group 3) So, comparing Be and Al, you find the values are (by chance) ex___ the s___. The increase from Group 2 to Group 3 is of___ by the fall as you go down Group 3 from boron to aluminium. Something similar happens from lithium (1.0) to magnesium (1.2), and from boron (2.0) to silicon (1.8). In these cases, the electronegativities aren't exactly the same, but are very close. Similar e_________ between the members of these diagonal pairs means that they are likely to form similar types of b__, and that will affect their chemistry.

equally electronegative half way molecular orbital

If the atoms are ______ _________, both have the same tendency to attract the bonding pair of electrons, and so it will be found on average* ___ ___between the two atoms. To get a bond like this, A and B would usually have to be the same atom. (eg. H2 or Cl2) (although C and H differ slightly in electronegativity, this small difference is negligible, and C-H bonds are considered ____. This sort of bond could be thought of as being a "pure" covalent bond -where the electrons are shared evenly between the two atoms *It is important to realize that this is an average picture. The electrons are actually in a ______ _____, and are moving around all the time within that orbital

not polar negative polar less electronegative positive

The molecule CCl4 (each bond is polar) is ____ ____ - in the sense that it doesn't have an end which is slightly positive and one which is slightly negative. The whole of outside of the molecule is slightly _____, but there is no overall separation of charge. By contrast, CHCl3 is ____. The hydrogen at the top is ____ _________ than carbon and so is slightly _____. Therefore, the molecule has a slightly positive "top" and a slightly negative "bottom", and so is overall a polar molecule.

Spectrum of bonds

The implication of ___ ___ is that there is no clear-cut division between covalent and ionic bonds. So how far does this dragging have to go before the bonds counts as ionic? There is no real answer to that. NaCl is a typical ionic solid, but even here the sodium hasn't completely lost control of its electron. But because of its properties, however, we tend to count it as if it were purely ionic. Lithium iodide, on the other hand, would be described as being ionic with some covalent character. In this case, the pair of electrons hasn't moved entirely over to the iodine end of the bond. For example, it dissolves in ____ _____ like ethanol - not something which ionic substances normally do.