According to the modern day model of the atom, the nucleus of an atom is surrounded by one or more

Answer is: electrons.

According to the Bohr model of the atom:

1. Electrons orbit the nucleus in orbits that have a set size and energy.

2. Energy levels of electrons are discrete (certain discrete values of energy).

3. Electrons can jump from one energy level to another, absorbing or emitting electromagnetic radiation with a frequency ν (energy difference of the levels).

The electron (symbol: e⁻) is a subatomic particle whose electric charge is negative one elementary charge.

Proton is a subatomic particle with a positive electric charge of +1e elementary charge.

Beside negatively charged electrons, atoms have positively charged protons, so atoms have neutral charge.

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answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.