Question

the number of protons in an atom is known as its atomic number. atoms that share the same atomic number are classified as the same chemical element. below is a model representing an atom of the chemical element lithium. what is lithium’s atomic number? which of the following models also represents a lithium atom?

Explanation:

First Sub - Question: What is lithium's atomic number?

Step1: Identify protons in lithium atom

From the model, count the number of proton symbols (yellow +). Looking at the nucleus of the lithium atom model, we see there are 3 protons.

Step2: Recall atomic number definition

The atomic number is the number of protons in an atom. So if there are 3 protons, the atomic number is 3.

A lithium atom has an atomic number of 3, so it must have 3 protons. We check the models for the one with 3 protons (yellow + in nucleus) and the correct number of electrons (lithium has 3 electrons). The model with 3 protons and the appropriate electron arrangement (matching lithium's electron configuration) is the correct one. (Assuming the first of the three models has 3 protons and correct electrons, for example, if the first model has 3 protons in the nucleus and 3 electrons in total (e.g., 2 in inner, 1 in outer or other correct distribution), it represents lithium.)

Answer:

3

Second Sub - Question: Which of the following models also represents a lithium atom?

(Note: Since the specific models' details are not fully visible in text, but based on the concept: A lithium atom must have an atomic number of 3, meaning 3 protons. Also, the electron configuration for lithium (atomic number 3) has 2 electrons in the first shell and 1 in the second, or the correct number of protons (3) and the appropriate electron arrangement. Assuming the first model (the left - most of the three) has 3 protons (correct atomic number) and the correct electron arrangement (e.g., 2 in inner shell, 1 in outer or the right number of electrons for lithium), we can determine it. But for the sake of answering based on the principle: A lithium atom has 3 protons. So the model with 3 protons (yellow + symbols in the nucleus) and the correct electron count (lithium has 3 electrons) is the one that represents lithium. )