Answer: a. two substances present; two phases present : Heterogeneous mixture
b. two substances present; one phase present
: Homogeneous mixture
c. one substance present; one phase present
: pure substance.
d. one substance present; two phases present: Heterogeneous mixture
Explanation:
A pure substance is a substance which contains definite composition of only one type of component. Hence, it cannot be separated by physical means.
Mixture is a substance which contains two or more than two types of components and they can be separated by physical means as well.
Homogeneous mixtures: It is a mixture that has uniform composition throughout the solution and the particle size or shapes are not different. There is no physical boundary between the dispersed phase and dispersion medium.
Heterogeneous mixtures: It is a mixture that has non-uniform composition throughout the solution and the particle size or shapes are also different. There is a physical boundary between the dispersed phase and dispersion medium.
Answer: Out of 118 elements, 94 occur naturally
Energy levels inside an are the specific that electrons can have when occupying specific orbitals. Electrons can be excited to higher by absorbing from the surroundings. Light is emitted when an electron relaxes from a high state to a lower one.
Answer:
- Please, find the drawing in the picture attached.
Explanation:
A simple model or drawing of the structure of an atom may be performed showing the electrons on the different energy levels (shells), plus the nucleons (protons and neutrons).
Then, you need the information on:
- number of protons (atomic number)
- electron configuration
- number of neutrons
The first step is to find the atomic number of the atom. You find that information in the periodic table, where the elements are show with their chemical symbol.
The chemical symbol of sodium is Na. It is located in the group (colum) 1 and period (raw) 3. There you find that the atomic number is 11. Hence your drawing must show 11 protons.
Since the atom is neutral, the number of electrons is also 11. So, you must place the electrons in the following energy levels or shells:
Main energy level shell number of electrons
n = 1 K 2 (this is the maximum in this level)
n= 2 L 8 (this is the maximun in this level)
n= 3 M 1 (the maximum in this level is 18)
Now that you have the number of protons and the location of the electrons, you must determine the number of neutrons.
In the periodict table you will also find the atomic mass of the elements. The atomic mass of sodium is 22.990 amu. That means that most sodium atoms have mass number (number of protons plus neutrons) 23. Some isotopes will have less neutrons, but you can draw your model using the most typical isotope with 23 nucleons. This means, that the number of neutrons is 23 nucleons - 11 protons = 12 neutrons.