Question

an element has an atomic number of 45 and an atomic mass of 98. how many neutrons does it have?
45
53
98
an element has an atomic number of 39 and a charge of -2. how many electrons does this element have?
2
37
39
41
an atom has a charge of -3. which statement best explains how this happened:
the neutral atom of the element gained 3 electrons
the neutral atom of the element lost 3 electrons
the neutral atom of the element gained 3 protons
the neutral atom of the element lost 3 protons

Explanation:

First Question:

Step1: Recall the formula for neutrons

The formula for calculating the number of neutrons is \( \text{Number of neutrons}=\text{Atomic mass}-\text{Atomic number} \).

Step2: Substitute the given values

Given atomic number \( Z = 45 \) and atomic mass \( A=98 \). Then \( \text{Number of neutrons}=98 - 45=53 \).

Second Question:

Step1: Recall the relationship between atomic number, charge and electrons

The atomic number \( Z\) is equal to the number of protons. For a neutral atom, the number of electrons \( e=\text{Number of protons}\). If the charge \( q=- 2\), then \( q=e-\text{Number of protons}\).

Step2: Substitute the values

Let the number of protons \( p = 39\) (since atomic number \( Z = 39\)). We know \( q=e - p\), so \( - 2=e-39\). Solving for \( e\), we get \( e=39+( - 2)+2=41\) (because \( e=p + q\), \( e = 39+( - 2)=37\) is wrong, actually \( q=\text{Electrons}-\text{Protons}\), so \( \text{Electrons}=\text{Protons}+|q|\) when \( q<0\)).

Third Question:

Step1: Recall the charge - electron relationship

Electrons are negatively charged (\( - 1\) charge per electron) and protons are positively charged (\(+1\) charge per proton). A neutral atom has equal number of protons and electrons.

Step2: Analyze the charge change

If an atom has a charge of \( - 3\), it means it has gained 3 electrons (because each electron adds a \( - 1\) charge. Gaining electrons makes the atom negatively charged, while losing electrons makes it positively charged. Protons are in the nucleus and are not easily lost or gained in chemical reactions that form simple ions)

Answer:

1. \(53\)
2. \(41\)
3. The neutral atom of the element gained 3 electrons.