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olasank [31]
3 years ago
7

Use the helium-4 isotope to define atomic number and mass number. why does knowledge of atomic number enable us to deduce the nu

mber of electrons present in an atom
Chemistry
1 answer:
Nuetrik [128]3 years ago
8 0
Helium - 4 isotope has 2 protons and 2 neutrons.

Its atomic number is 2 (the number of protons). Atomic number is the number of protons in the atom of an element and it identifies the element. All the isotopes of an element have the same atomic number (same number of protons). So, all the isotopes of hellium have 2 protons.

The number 4 that identifies the helium - 4 isotope is the mass number, i.e. the number of protons plus the number of neutron. So, helium-4 isotope has 2 protons and 2 neutrons. While, other isotopes of helium have 2 protons but different number of neutrons.

The atomic number enable us to deduce the number of electrons in an atom because the atoms are neutral, which implies that the positive and negative charge are equal. Given that the magnitude of the charge of electons and protons are equal but the sign is opposed (protons are positve and electrons are negative) the number of electrons in the atom equals the number of protonts. That is why the atomic number is also the number of electrons of the atom.
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Describe three signs that a chemical reaction has taken place and give an example of each sign
il63 [147K]
Color change, temperature change, bubbling, state change

green to blue, hot to cold, bubbles (lol), and liquid to gas
7 0
3 years ago
Chlorine can be prepared in the laboratory by the reaction of manganese dioxide with hydrochloric acid. HCl(aq), as described by
melisa1 [442]

Answer:

0.88 g

Explanation:

Using ideal gas equation to calculate the moles of chlorine gas produced as:-

PV=nRT

where,

P = pressure of the gas = 805 Torr

V = Volume of the gas = 235 mL = 0.235 L

T = Temperature of the gas = 25^oC=[25+273]K=298K

R = Gas constant = 62.3637\text{torr}mol^{-1}K^{-1}

n = number of moles of chlorine gas = ?

Putting values in above equation, we get:

805torr\times 0.235L=n\times 62.3637\text{ torrHg }mol^{-1}K^{-1}\times 298K\\\\n=\frac{805\times 0.235}{62.3637\times 298}=0.01017\ mol

According to the reaction:-

MnO_2+4HCl\rightarrow MnCl_2+2H_2O+Cl_2

1 mole of chlorine gas is produced when 1 mole of manganese dioxide undergoes reaction.

So,

0.01017 mole of chlorine gas is produced when 0.01017 mole of manganese dioxide undergoes reaction.

Moles of MnO_2 = 0.01017 moles

Molar mass of MnO_2 = 86.93685 g/mol

So,

Mass=Moles\times Molar\ mass

Applying values, we get that:-

Mass=0.01017moles \times 86.93685\ g/mol=0.88\ g

<u>0.88 g of MnO_2(s) should be added to excess HCl (aq) to obtain 235 mL of Cl_2(g) at 25 degrees C and 805 Torr.</u>

6 0
3 years ago
What os the formula for hexaboron tetrabromide
LekaFEV [45]

Answer:

B6Br4

Explanation:

Chemical formula gives a representation of the number of atoms that each element in a compound or molecule. In this question which is asking to give the formula of hexaboron tetrabromide, the hexa means 6 while the tetra means four.

Since the number of atoms of each element is written as a prefix before the main element, this means that the chemical formula of hexaboron tetrabromide will be B6Br4.

6 0
3 years ago
After an organism ingests food, the food moves through a series of _______ by which it is broken down and rearranged to form new
Yakvenalex [24]

Answer:

metabolism

cell division

Explanation:

metabolism is the series of activities that take place in the body of an organism

cell division is the enlargement or division of cell in order for growth to occur

3 0
3 years ago
What is the overall reaction for photosynthesis? select one:
likoan [24]
Plants combine water and Carbon dioxide from the air to make glucose for themselves, and giving off oxygen in the process. So CO2 and H2O would be on ther reactant side (left) with O2 and C6H12O6 being on the product side (right).
3 0
3 years ago
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