Answer:

Explanation:
The question is asking to write the <em>isotopic symbol </em>of the form
for the <em>sodium isotope with 13 neutrons</em>.
In general, the isotopic symbol in the given form shows:
- The element's chemical symbol: X
- A: mass number of the isotope, written as a superscript to the left of the element's simbol, and
A = number of protons + number of neutrons
- Z: atomic number of the isotope, written as a subscript to the left of the elements's symbol,
Z = number of protons
The atomic symbol of sodium is Na.
The atomic number, or number of protons, is the same for every isotope of the element, and you can find it in any periodic table. Tha atomic number of sodium is 11. Thus:
The mass number is the number of protons plus neutrons, hence:
Now you can write the isotope symbol for the sodium isotope with 13 neutrons:

✧・゚: *✧・゚:* *:・゚✧*:・゚✧
Hello!
✧・゚: *✧・゚:* *:・゚✧*:・゚✧
❖ J.J Thomson was the first to discover atoms. He discovered atoms in 1897.
~ ʜᴏᴘᴇ ᴛʜɪꜱ ʜᴇʟᴘꜱ! :) ♡
~ ᴄʟᴏᴜᴛᴀɴꜱᴡᴇʀꜱ
2H2 + O2 ---> 2H2O
1 mole of H2 = 2g
1 mole of O2 = 32g
1 mole of H2O = 18g
according to the reaction:
2*2g H2---------------32g O2
1,6g H2----------------- x g O2
x = 12,8g O2
so reaction is stechiometric
32g O2---------------- 2*18g H2O
12,8g O2 -------------- x
x = 14,4g H2O
answer: 14,4g of water vapour
<span>The
scientist thought that the atom was the smallest particle in the universe is
John Dalton. He established the atomic theory which
consists of five; elements are made of extremely small particles called atoms,
atoms of different element have different sizes, mass and physic – chemical
properties, atoms cannot be divided further, destroyed or created, atoms can
combine to form compounds and in chemical reaction, atoms can be combined,
separated or rearranged</span>
Answer:

Explanation:
Calcium is the element of the group 2 and period 4 which means that the valence electronic configuration is
.
Chlorine is the element of the group 17 and period 3 which means that the valence electronic configuration is
.
Thus, calcium losses 2 electrons to 2 atoms of chlorine and these 2 atoms of chlorine accepts each electron to form ionic bond. This is done in order that the octet of the atoms are complete and they become stable.
Ca Cl
2 1
Cross multiplying the valency, We get, 
Thus, the formula of calcium chloride is
.