Answer:
Mendeleev left gaps in his periodic table because he knew that these elements existed, but had not yet been discovered. He believed that the elements would be eventually found and would fit perfectly into the gaps. Two such elements are Germanium and Gallium.
Explanation:
Mass was conserved, because it was losing all shape, weight, and matter. It really has no mass.
Explanation:
heliocentric means having the sun in the middle/center in the solar system
geocentric means having the earth in the middle/center in the solar system
therefore your answers are:
the planets orbit the sun.
in 1543, Nicolaus Copernicus proposed the theory.
the evidence that led people to believe this was when Galileo observed that four moons orbited around Jupiter. in other words, heliocentric.
most of the stars are located in the milky way galaxy.
Answer:
Explanation:
Substance are consist of very large number of atoms, ions , molecules etc.
They can not be count in a simple way. Scientist used Avogadro number to express the large number of atoms, ions, molecules.
Avogadro number:
It is the number of atoms , ions and molecules in one gram atom of element, one gram molecules of compound and one gram ions of a substance.
The number 6.022 × 10²³ is called Avogadro number.
For example,
18 g of water = 1 mole = 6.022 × 10²³ molecules of water
1.008 g of hydrogen = 1 mole = 6.022 × 10²³ atoms of hydrogen
96.06 g of SO₄²⁻ ion = 1 mole of SO₄²⁻ ion = 6.022 × 10²³ ions of SO₄²⁻
Answer:
since, atomic number=no. of electrons
atomic number :5 =no. of electrons: 5
atomic number :7 =no. of electrons: 7
