How many protons,neutrons and electrons are present in an atom of hafnium,hf,with a mass number of 178?

Chemistry

2 answers:

AleksAgata [21]3 years ago

7 0

178 of each species
178 protons
178 neutrons
And 178 electrons

AlladinOne [14]3 years ago

4 0

Answer:

72 protons

102 neutrons

72 electrons

Explanation:

Hf has an atomic number of 72. By definition, this means that it has 72 protons.

It also has a mass number of 178. The mass number (A) counts all elements with significant mass (protons and neutrons). Then,

A = p⁺ + n⁰

n⁰ = A - p⁺ = 178 - 72 = 102

Hf has 102 neutrons.

Elemental Hafnium is electrically neutral because it has the same amount of positive charges (protons) and negative charges (electrons). Then, it must have 72 electrons.

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RUDIKE [14]

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5 0

3 years ago

The half-life of radioactive substance is 2.5 minutes. what fraction of the origional radioactive remains after 10 mins

saul85 [17]

The answer is 1/16.

Half-life is the time required for the amount of a sample to half its value.
To calculate this, we will use the following formulas:
1. $(1/2)^{n} = x$ ,
where:
n - a number of half-lives
x - a remained fraction of a sample

2. $t_{1/2} = \frac{t}{n}$
where:
 $t_{1/2}$ - half-life
t - total time elapsed
n - a number of half-lives

So, we know:
t = 10 min
 $t_{1/2}$ = 2.5 min

We need:
n = ?
x = ?

We could first use the second equation to calculate n:
If:
$t_{1/2} = \frac{t}{n}$ ,
Then:
$n = \frac{t}{ t_{1/2} }$
⇒ $n = \frac{10 min}{2.5 min}$
⇒ $n=4$ 

Now we can use the first equation to calculate the remained fraction of the sample.
 $(1/2)^{n} = x$
⇒ $x=(1/2)^4$
⇒ $x= \frac{1}{16}$