All categories

3 years ago

How many electrons does Helium (He) have?

2 answers:

6 0

Helium has two electrons. This can be found by looking at the atomic number on the periodic table. Neutral atoms have the same number of protons as electrons.

myrzilka [38]3 years ago

5 0

Answer: 2

Explanation:

Hope this helps! (^-^)

You might be interested in

When ammonium phosphate and nickel(ii) nitrate solutions are mixed, what precipitates out?

Sphinxa [80]

2(NH4)3PO4 (aq) + 3Ni(NO3)2(aq) ------> Ni3(PO4)2(s) + 6NH4NO3 (aq)

Ni3(PO4)2 is a precipitate.

5 0

3 years ago

Read 2 more answers

The unit cell for cr2o3 has hexagonal symmetry with lattice parameters a = 0.4961 nm and c = 1.360 nm. If the density of this ma

IRINA_888 [86]

To calculate the packing factor, first calculate the area and volume of unit cell.

Area is calculated as:

$A=6R^{2}\sqrt{3}$

Here, R is radius and is related to a as follows:

$R=\frac{a}{2}$

Putting the value in expression for area,

$A=6(\frac{a}{2})^{2}\sqrt{3}=1.5a^{2}\sqrt{3}$

The value of a is 0.4961 nm

Since, $1 nm=10^{-7}cm$

Thus, $0.4961 nm=4.961\times 10^{-8} cm$

Putting the value,

$Area=1.5(4.961\times 10^{-8}cm)^{2}\sqrt{3}=6.39\times 10^{-15}cm^{2}$

Now, volume can be calculated as follows:

$V=Area\times c$

The value of c is 1.360 nm or $1.360\times 10^{-7} cm$

Putting the value,

$V=(6.39\times 10^{-15}cm^{2})\times (1.360\times 10^{-7} cm)=8.7\times 10^{-22}cm^{3}$

now, number of atom in unit cell can be calculated by using the following formula:

$n=\frac{\rho N_{A}V_{c}}{A}$

Here, A is atomic mass of $Cr_{2}O_{3}$ is 151.99 g/mol.

Putting all the values,

$n=\frac{(5.22 g/cm^{3})(6.023\times 10^{23} mol^{-1})(8.7\times 10^{-22}cm^{3})}{(151.99 g/mol)}\approx 18$

Thus, there will be 18 $Cr_{2}O_{3}$ units in 1 unit cell.

Since, there are 2 Cr atoms and 3 oxygen atoms thus, units of chromium and oxygen will be 2×18=36 and 3×18=54 respectively.

The atomic radii of $Cr^{3+}$ and $O^{2-}$ is 62 pm and 140 pm respectively.

Converting them into cm:

$1 pm=10^{-10}cm$

Thus,

$r_{Cr^{3+}}=6.2\times 10^{-9}cm$

and,

$r_{O^{2-}}=1.4\times 10^{-8}cm$

Volume of sphere will be sum of volume of total number of cations and anions thus,

$V_{S}=V_{Cr^{3+}}+V_{O^{2-}}$

Since, volume of sphere is $V=\frac{4}{3}\pi r^{3}$ ,

$V_{S}=36\left ( \frac{4}{3}\pi (r_{Cr^{3+})^{3}} \right )+54\left ( \frac{4}{3}\pi (r_{O^{2-})^{3}} \right )$

Putting the values,

$V_{S}=36\left ( \frac{4}{3}(3.14) (6.2\times 10^{-9} cm)^{3}} \right )+54\left ( \frac{4}{3}(3.14) (1.4\times 10^{-8} cm)^{3}} \right )=6.6\times 10^{-22}\times 10^{-8}cm^{3}$

The atomic packing factor is ratio of volume of sphere and volume of crystal, thus,

$packing factor=\frac{V_{S}}{V_{C}}=\frac{6.6\times 10^{-22}cm^{3}}{8.7\times 10^{-22}cm^{3}}=0.758$

Thus, atomic packing factor is 0.758.

6 0

3 years ago

Read 2 more answers

For which purpose do biochemists insert human genes into bacteria?

forsale [732]

Insertion of human genes into bacteria, also known as recombinant DNA technology, is used for the large scale production of human insulin, using bacteria as the insulin-producing machinery. The gene containing information for insulin production is inserted into the DNA of bacteria, which transcribe and translate it, and insulin is produced.

7 0

3 years ago

Read 2 more answers

In a certain electrolysis experiment, 1.24 g of Ag were deposited in one cell (containing an aqueous AgNO3 solution), while 0.65

eduard

Answer:

The correct answer is 169.56 g/mol.

Explanation:

Based on the given information, the mass of Ag deposited is 1.24 g, and the mass of unknown metal X deposited in another cell is 0.650 g. The number of moles of electrons can be determined as,

= 1.24 g Ag * 1mol Ag/107.87 g/mol Ag * 1 mol electron/1 mol Ag ( the molecular mass of Ag is 107.87 g/mol)

= 0.0115 mole of electron

The half cell reaction for the metal X is,

X^3+ (aq) + 3e- = X (s)

From the reaction, it came out that 3 faraday will reduce one mole of X^3+.

The molar mass of X will be,

= 0.650 g/0.0115 *3 mol electron/1 mol

= 56.52 * 3

= 169.56 g/mol

7 0

3 years ago

Xenon forms several compounds with oxygen and fluorine. It is the most reactive non-radioactive noble gas because a. its large r

muminat

Answer:

d. its effective nuclear charge is lower than the other noble gases.

Explanation:

Xenon belongs to group O on the periodic table. Most of the elements here are unreactive.

Due to the large size of Xenon, the outermost electrons have very low effective nuclear charge. Effective nuclear charge is the effect of the positive charges of the nucleus on the electrons in orbits. This effect decreases outward as atomic shell increases.

Xenon has a very large atomic radius and there is weak a nuclear charge on the outermost electrons. The more electronegative elements would be able to attract some of its outermost electrons easily and form chemical bonds with xenon much more readily.

7 0

3 years ago