# 18.3 Structure and general properties of the metalloids  (Page 4/10)

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$\text{2NaF}\left(s\right)+{\text{SiF}}_{4}\left(g\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{Na}}_{2}{\text{SiF}}_{6}\left(s\right)$

Antimony reacts readily with stoichiometric amounts of fluorine, chlorine, bromine, or iodine, yielding trihalides or, with excess fluorine or chlorine, forming the pentahalides SbF 5 and SbCl 5 . Depending on the stoichiometry, it forms antimony(III) sulfide, Sb 2 S 3 , or antimony(V) sulfide when heated with sulfur. As expected, the metallic nature of the element is greater than that of arsenic, which lies immediately above it in group 15.

## Boron and silicon halides

Boron trihalides—BF 3 , BCl 3 , BBr 3 , and BI 3 —can be prepared by the direct reaction of the elements. These nonpolar molecules contain boron with sp 2 hybridization and a trigonal planar molecular geometry. The fluoride and chloride compounds are colorless gasses, the bromide is a liquid, and the iodide is a white crystalline solid.

Except for boron trifluoride, the boron trihalides readily hydrolyze in water to form boric acid and the corresponding hydrohalic acid. Boron trichloride reacts according to the equation:

${\text{BCl}}_{3}\left(g\right)+{\text{3H}}_{2}\text{O}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{B}{\text{(OH)}}_{3}\left(aq\right)+\text{3HCl}\left(aq\right)$

Boron trifluoride reacts with hydrofluoric acid, to yield a solution of fluoroboric acid, HBF 4 :

${\text{BF}}_{3}\left(aq\right)+\text{HF}\left(aq\right)+{\text{H}}_{2}\text{O}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{H}}_{3}{\text{O}}^{\text{+}}\left(aq\right)+{\text{BF}}_{4}{}^{\text{−}}\left(aq\right)$

In this reaction, the BF 3 molecule acts as the Lewis acid (electron pair acceptor) and accepts a pair of electrons from a fluoride ion:

All the tetrahalides of silicon, SiX 4 , have been prepared. Silicon tetrachloride can be prepared by direct chlorination at elevated temperatures or by heating silicon dioxide with chlorine and carbon:

${\text{SiO}}_{2}\left(s\right)+\text{2C}\left(s\right)+{\text{2Cl}}_{2}\left(g\right)\phantom{\rule{0.2em}{0ex}}\stackrel{\phantom{\rule{0.4em}{0ex}}\text{Δ}\phantom{\rule{0.4em}{0ex}}}{\to }\phantom{\rule{0.2em}{0ex}}{\text{SiCl}}_{4}\left(g\right)+\text{2CO}\left(g\right)$

Silicon tetrachloride is a covalent tetrahedral molecule, which is a nonpolar, low-boiling (57 °C), colorless liquid.

It is possible to prepare silicon tetrafluoride by the reaction of silicon dioxide with hydrofluoric acid:

${\text{SiO}}_{2}\left(s\right)+\text{4HF}\left(g\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{SiF}}_{4}\left(g\right)+{\text{2H}}_{2}\text{O}\left(l\right)\phantom{\rule{5em}{0ex}}\text{Δ}H\text{°}=\text{−191.2 kJ}$

Hydrofluoric acid is the only common acid that will react with silicon dioxide or silicates. This reaction occurs because the silicon-fluorine bond is the only bond that silicon forms that is stronger than the silicon-oxygen bond. For this reason, it is possible to store all common acids, other than hydrofluoric acid, in glass containers.

Except for silicon tetrafluoride, silicon halides are extremely sensitive to water. Upon exposure to water, SiCl 4 reacts rapidly with hydroxide groups, replacing all four chlorine atoms to produce unstable orthosilicic acid, Si(OH) 4 or H 4 SiO 4 , which slowly decomposes into SiO 2 .

## Boron and silicon oxides and derivatives

Boron burns at 700 °C in oxygen, forming boric oxide, B 2 O 3 . Boric oxide is necessary for the production of heat-resistant borosilicate glass, like that shown in [link] and certain optical glasses. Boric oxide dissolves in hot water to form boric acid, B(OH) 3 :

${\text{B}}_{2}{\text{O}}_{3}\left(s\right)+{\text{3H}}_{2}\text{O}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{2B}{\text{(OH)}}_{3}\left(aq\right)$

An atom or group of atoms bearing anelectrical charge such as the sodium and chlorine atoms in a salt solution.
Hello guys! Answer me questions nah
pls wat is periodic table
Prince
it's a list that shows the chemical element arranged according to their properties.
what is the chemical equation for ideal gas?
what's Boyle and gas law?
what's the meaning of this℃ in atomic table
wat are ions
Sinyene
What is periodic table
Table that shows the elements in order of their atomic number
Uzair
organization of everything known in the universe in groups and periods. The structure is based on increasing mass and reaction properties.
Kate
How to mix chemical
why the elements of group 7 are called Noble gases
they aren't. group 8 is the noble gasses. they are snobs that don't mix with others like nobles, they have full valence shells so they don't form bonds with other elements easily. nobles don't mingle with the common folk...
Jessica
the group 7elements are not the noble gases . according to modern periodic group 18 are called noble gases elements because their valence shell are completely field so that they can't gain or loss electron so they are not able to involve in any chemical reaction.
Leena
Group 7 element they are not noble gases they halogen and halogen mean salt formers
SIRAJO
what is chemistry
chemistry is the branch of science which deal with the composition of matter
SHEDRACK
chemistry is an organized way to think about matter
Kate
Chemistry is the branch of science that deals with the composition, properties and uses of matter
Bamgbose
The branch of science concerned with the substances of which matter is composed, the investigation of their properties and reactions, and the use of such reactions to form new substances.
Aminu
discuss the orbital stracture of the following methane,ethane,ethylene,acetylene
Why phosphurs in solid state have one atom but in gas state have four atoms
Are nuclear reactions both exothermic reactions and endothermic reactions or what?
to what volume must 8.32 NaOH be diluted to its analytical concentration 0.20 M
weight in mg 1.76 mole of I
Sheriza
the types of hydrocarbons
u are mad go and open textbook
Emmanuel
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Jessica
aliphatic and aromatic hydrocarbons
Osakue
stupid boy Emmanuel
Ohanaka
saturated and unsaturated
Leena
aromatic hydrocarbon aliphatic hydrocarbon
SIRAJO
I don't use to see the messages
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SIRAJO
how can you determine the electronegativity of a compound or in molecules
when u move from left to right in a periodic table the negativity increases
reeza
Are you trying to say that the elctronegativity increases down the group and decreases across the period?
Ohanaka
yes and also increases across the period
reeza
for instance when you look at one group of elements in a periodic table electronegativity decreases when you go across the table electronegativity increases. hydrogen is more electronegative than sodium, potassium of that group. oxygen is more electronegative than carbon.
reeza
i hope we all know that organic compounds have carbon as their back bone
OK,Thank you so much for the answer. I am happy now
can I ask you a question now
Osakue
yes
hanna
what is the oxidation number of nitrogen, oxygen and sulphur
Osakue
5, -2 & -2
hanna
What is periodic table
SIRAJO
What is an atom?
is a smallest particle of a chemical element that can exist
Osakue
Osakue
it is a substance that cannot be broken down into simpler units by any chemical reaction
An atom is the smallest part of an element dat can take part in chemical reaction.
Idris
an atom is the smallest part of an element that can take part in a chemical reaction nd still retain it chemical properties
Precious
Is the smallest particles of an element that take part in chemical reaction without been change
John