The first atoms and first molecule (helium hydride) formed several hundred thousand years after the Big Bang. The first generation of stars followed 180 million years later. N.R.Fuller, National Science Foundation
Trillions of degrees. That was the temperature a fraction of a second after the Big Bang. So darn hot it took 380,000 years for it to cool down enough for individual protons and neutrons to come together to form the first atoms. Cool is a relative term. The temperature at the time simmered around 6,700° F (3,700° C), not exactly a spring afternoon. About three-quarters of those early atoms were hydrogen, the simplest element, and most of the remainder helium.
Most of the early universe was made of the simplest atoms, hydrogen and helium. The red balls inside each atom are protons; the blue ones are neutrons. NASA / Ames Research Center
Hydrogen is the simplest atom with a single positively-charged proton for a nucleus orbited by a negatively-charged electron. Helium has two protons and two neutral particles called neutrons in its core orbited by two electrons. Atoms join together to form molecules. When lots of atoms join in a variety of ways, complex molecules result.
Structure of human ...