## What is the meaning of A mass number shown in parenthesis?

If the atomic mass of a particular element is shown in parentheses, such as (145) for Promethium (Pm), the atomic mass reflects that of the most stable isotope1, and is not the average atomic mass for all isotopes of the element. Atomic masses used on this periodic table are from the IUPAC 1995 recommendations.

## Why are the masses of some listed as whole numbers in parentheses?

If an element has no stable isotopes, meaning that all known isotopes of that element will undergo nuclear decay, the atomic number is displayed in parentheses.

## What is the meaning of A mass number?

Mass number, in nuclear physics, the sum of the numbers of protons and neutrons present in the nucleus of an atom.

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## What does it mean when an element has brackets?

Very often in chemical formulae, we use parentheses to form subgroups of atoms within a molecule. In such a formula, the subscript outside the parentheses means that to count atoms, you must multiply that subscript by the numbers of atoms inside.

## How many atoms are in a human body?

Suzanne Bell, an analytical chemist at West Virginia University, estimates that a 150-pound human body contains about 6.5 octillion (that’s 6,500,000,000,000,000,000,000,000,000) atoms. The vast majority of them are hydrogen (humans are almost entirely water, which comprises two hydrogen atoms and an oxygen).

## What is the meaning of a mass number shown in parentheses quizlet?

What is the meaning of a mass number showing parenthesis? The mass number is the sum of the number of protons and neutrons its nucleus.

## Can the average atomic mass be a whole number?

Atomic mass is never an integer number for several reasons: The atomic mass reported on a periodic table is the weighted average of all the naturally occuring isotopes. Being an average it would be most unlikely to be a whole number. The mass of an individual atom in atomic mass units is the mass relative to carbon-12.

## Why is the atomic mass of boron 10.81 and not rounded to 11?

The atomic mass of boron is 10.81 u. And 10.81 u is a lot closer to 11u than it is to 10u, so there must be more of boron-11. Where u is the unit for atomic mass and x is the proportion of boron-10 out of the total boron abundance which is 100%. And thus the abundance of boron-11 is roughly 81%.

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## What element is at the top of the activity series?

The elements at the top of the activity series are in Groups 1 and 2 of the Periodic Table. Here is a picture of the activity series. The top seven elements in the list are Li, Na, K, Mg, Ca, Sr, and Ba. These are all in Groups 1 and 2 of the Periodic Table.

## What’s an example of a mass number?

The total number of protons and neutrons in the nucleus of an atom. For example, nitrogen has 7 protons and 7 neutrons in its nucleus, giving it a mass number of 14. Isotopes of elements are distinguished by their mass number; for example, carbon-12 and carbon-14 have mass numbers of 12 and 14 respectively.

## What is the best definition of mass number?

Mass number is an integer (whole number) equal to the sum of the number of protons and neutrons of an atomic nucleus. In other words, it is the sum of the number of nucleons in an atom. Mass number is often denoted using a capital letter A.

## What is the example of mass number?

(ii) Mass number: It is the sum of the number of neutrons and the number of protons. For example, the atomic number of Lithium is 4 which is equal to the number of protons, the number of neutrons of magnesium is 4. The mass number is equal to 8(4+4).

## Why is atomic weight in parentheses?

The atomic weight of an element is based on the variety of naturally occurring isotopes of that element and the relative abundance of each. These elements are unstable; that is, their nuclei decompose radioactively. The number in parentheses is the mass number of the most stable or best-known isotope of that element.

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## Do square brackets mean concentration?

Square brackets are often used to represent concentration, e.g., [NaOH] = 0.50 M. Use the capital letter M for molarity, not a lower case m (this is a different concentration unit called molality).

## Why do we put brackets around elements that have charges?

If there’s more than one complex ion in the compound, then brackets are needed. The reason is that you need to put a bracket around the complex ion to show how many of those whole complex ions there are in the compound.