1. What causes shadows?

Write the atomic symbol for the isotope of bismuth with 125 neutrons.

vlada-n [284]

First, isotopes are the atoms of a single element whose nuclei have a different number of neutrons, and therefore, differ in mass numbers. You should know that atoms are formed by a nucleus that has a small size and is made up of protons and neutrons. The nucleus is surrounded by a cloud of electrons, which are found in a region of the atom called the cortex.

The mass number, represented as A, is the sum of the number of protons and neutrons in the nucleus. On the other hand, the atomic number (Z) is the number of protons that exist in the nucleus.

The isotopes of an element X are represented as follows,

(see first attached picture)

It should be noted that the number of neutrons of a chemical element can be calculated as the difference A-Z.

The atomic and mass numbers of bismuth with 125 neutrons are:

Z = 83

A = 83 + 125 = 208

Thus, the atomic symbol of the bismuth isotope with 125 neutrons is:

(see second attached picture)

5 0

3 years ago

Explain why ionic compound do not form molecules.

Darina [25.2K]

Answer:

Because a molecule, by definition, has a valence of zero

(neutral charge, stable). Also by definition, an ion has a positive

or negative charge or valence and is not stable.

Explanation:

7 0

3 years ago

1.) When blood flow is gone from the extremities for too long, the cells start to die. Depending on the severity of the

valkas [14]

Answer:

its A

Explanation:

because frostbite kills the nerves

5 0

2 years ago

At standard pressure, ammonia melts at 195 K and boils at 240 K. If a sample of ammonia at standard pressure is cooled from 200

Svetradugi [14.3K]

Answer:

I) the heat capacity of ammonia(s)

II) the heat capacity of ammonia(ℓ)

IV) the enthalpy of fusion of ammonia

Explanation:

Initially, ammonia at 200 K is liquid. To calculate the change of enthalpy from 200 K to 195 K (melting point) we need to know the heat capacity of ammonia(ℓ).

At 195, ammonia is in the transition from liquid to solid (solidification). To calculate the change of enthalpy in that process we need to know the enthalpy of solidification of ammonia, which has the same value but opposite sign to the enthalpy of fusion of ammonia.

From 195 K to 0 K, ammonia is solid. To calculate the change of enthalpy in that process we need to know the heat capacity of ammonia(s).

7 0

3 years ago

Copper can have improved wear resistance if alloyed with ceramic alumina, Al2O3. If a copper alloy has 7.7 wt % Al2O3, what is i

vitfil [10]

The composition in mol% of the elements are :

4.91% of Al₂O₃ in alloy
95.08% of Cu in alloy

Given data :

Weight percentage of copper alloy = 7.7 wt %

Assume weight of alloy = 100 grams

<h3>Applying the weight percentage </h3>

mass of Al₂O₃ in alloy = 7.7 gm

Mass of Cu in alloy = 100 - 7.7 = 92.3 gm

First step : calculate the mole of elements

i) moles of Al₂O₃ in alloy

= mass of Al₂O₃ in alloy / Atomic mass of Al₂O₃

= 7.7 gm / 102 gm/mol

= 0.075 mol

ii) moles of Cu in alloy

= mass of Cu in alloy / Atomic mass of Cu

= 92.3 gm / 63.5 gm/mol

= 1.45 mol

Therefore the total number of moles in the alloy = 0.075 + 1.45 = 1.525

Next step : Determine the mole percentages

i) Mole percentage of Al₂O₃ in alloy

= ( 0.075 ) / 1.525 * 100

= 4.91%

ii) Mole percentage of Cu in alloy

= ( 1.45 ) / 1.525 * 100

= 95.08%

Hence we can conclude that The composition in mol% of the elements are : 4.91% of Al₂O₃ in alloy and 95.08% of Cu in alloy.

Learn more about alloys : brainly.com/question/716507

4 0

2 years ago