Boron trifluoride has a bond angle of 120 degrees.

180°

trigonal

A simple example: phosphorus(V) fluoride, PF5 The 5 electron pairs take up a shape described as a trigonal bipyramid – three of the fluorines are in a plane at 120° to each other; the other two are at right angles to this plane. The trigonal bipyramid therefore has two different bond angles – 120° and 90°.

The bond angle is 90 degrees. For example, sulfur hexafluoride (SF6) is an octahedral molecule. Trigonal pyramidal: A trigonal pyramidal molecule has a pyramid-like shape with a triangular base.

A bond angle is the angle between any two bonds that include a common atom, usually measured in degrees. A bond distance (or bond length) is the distance between the nuclei of two bonded atoms along the straight line joining the nuclei.

Lone pair repulsion: Bond angle is affected by the presence of lone pair of electrons at the central atom. A lone pair of electrons at the central atom always tries to repel the shared pair (bonded pair) of electrons. Due to this, the bonds are displaced slightly inside resulting in a decrease of bond angle.

VSEPR Theory: Valence Shell Electron Pair Repulsion Theory. VSEPR theory predicts methane is a perfect tetrahedron with all H-C-H bond angles equal at 109.5o, because the hydrogen atoms repel equally, and because this geometry puts the greatest distance between all four bonded electrons pairs.

109°

two C

Why does this question apply to Table 3? The 2 most electronegative elements on the periodic table are Fluorine and Oxygen. This question applies to part 3 because all of the molecules except one uses fluorine and oxygen which means that they are all mostly electronegativity.

Again, that’s FONCLBRISCH. This is the most electronegative elements on the periodic table starting with the most electronegative on the top, and decreasing in electronegativity as we work down. So we have fluorine, oxygen, nitrogen, chlorine, bromine, iodine, sulfur, carbon, and hydrogen.

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. But oxygen has 8 protons in the nucleus whereas nitrogen only has 7. A bonding pair will experience more attraction from the oxygen’s nucleus than from nitrogen’s, and so the electronegativity of oxygen is greater.

Fluorine (shown in red) is the most electronegative (least electropositive) element (EN = 4.0). Cesium and francium (shown in blue) are the least electronegative (most electropositive) elements (EN = 0.7).

Potassium (K) is more electropositive than sodium (Na). So potassium is below sodium with greater atomic number.

Sodium is more electropositive than hydrogen although they are in the same group.

Noble gases

Reactivity Trend in the Periodic Table

• The most reactive element is fluorine, the first element in the halogen group.
• The most reactive metal is francium, the last alkali metal (and most expensive element).
• The least reactive elements are the noble gases.

Silver, gold, and platinum are metals with the least reactivity. They are found in nature.

Hydrogen

Alkali metals (situated far away from transitional metals and noble gases) are the most reactive elemental group. Cesium is second from the bottom of this group, with 6 electron shells, so it fits all the characteristics of a reactive atom, therefore making it the most reactive element.

Sodium on the opposite side of the table has the opposite properties. Its single outer electron makes the metal highly reactive and ready to combine with others at the first opportunity – such as the moment the metal hits water.

An element that is highly electronegative, such as fluorine, has an extremely high attraction for bonding electrons. Elements at the opposite end of the spectrum, such as highly reactive metals cesium and francium, readily form bonds with electronegative atoms.

Cesium

Humans may be exposed to cesium by breathing, drinking or eating. In air the levels of cesium are generally low, but radioactive cesium has been detected at some level in surface water and in many types of foods.

Caesium (cesium in USA) metal reacts rapidly with water to form a colourless solution of caesium hydroxide (CsOH) and hydrogen gas (H2). The resulting solution is basic because of the dissolved hydroxide. The reaction is very exothermic.

HIGHLIGHTS: Exposure to stable or radioactive cesium occurs from ingesting contaminated food or drinking water or breathing contaminated air. High levels of radioactive cesium in or near your body can cause nausea, vomiting, diarrhea, bleeding, coma, and even death.

: a metallic chemical element that is the most electropositive element known and that is used in photoelectric cells, in atomic clocks, and as a component of drilling fluid — see Chemical Elements Table.

Sodium

Magnesium, lithium, sodium, potassium, caesium, and rubidium are all metals that will burn and react with water.